A minute’s silence – a chance to listen to the wind and the waves crashing on to shingle, and look across the Solent to the lights of a cruise ship in the distance – and then we charge into the water, although some of us (me) are more tentative. There are shrieks and gasps from the shock of the cold; grimacing, grinning faces lit up by a portable floodlight.

It is barely 6am, and still dark. It’s also the windiest, rainiest weather this group has ventured out in, but an impressively hardy 12 have turned up. On a good day, about 30 meet each Friday at 5.30am in Gosport, Hampshire, for a two-mile walk along Stokes Bay, followed by a dip in the sea. “It has changed my life,” says one man, who has been coming since the group started last year. He says meeting strangers, and the welcoming atmosphere, has allowed him to open up about his mental health and seek some help. Kerry started coming in October last year and says the weekly meet has helped relieve the seasonal affective disorder she usually suffers from at this time of year. “I used to sleep for 10, 11 hours,” she says. “If you had told me last year I’d be getting up at this time each week to do this, I wouldn’t have believed it.”

The group – Win the Morning, Win the Day – was set up in August last year by Chris Reeves, a physical training instructor in the Royal Navy. He had struggled with isolation and lack of structure to his days throughout the first lockdown, and knew others must be feeling the same. After hearing a podcast with the mixed martial arts fighter Mark Scanlon, talking about the 5.30am circuit training sessions and sea swims he was running in Liverpool, Reeves decided to create his own. Scanlon used the phrase “win the morning, win the day”, which is what Reeves decided to call the group. It’s a mantra popularised by the US entrepreneur and productivity guru Tim Ferriss, which has become popular in motivational circles. Ferriss interviewed a wealth of high-achieving people about their morning routine, with the idea that if you get your morning right (if you “win” it), it’s a good start to the rest of the day. His own morning rituals include making his bed and journaling; for the Gosport group, it’s more about walking, talking, stripping off, going for a quick dip, then having coffee and more chat afterwards.

In the first week, just over a year ago, 60 people turned up to join Reeves. His group has since spawned others in Surrey, Kent, Preston, Cumbria, Manchester, and Southsea, across the water in Portsmouth. There’s one in Gibraltar, he says, and another in South Africa. Two people have been in touch with Reeves this week to talk about setting up groups. It’s a little like parkrun, the 5km run that takes place in parks around the world every weekend – a simple idea, organised by enthusiastic volunteers.

Why does Reeves think Win the Morning, Win the Day is taking off? “It’s free, I’m not selling anything and it’s a welcoming environment for anyone who wants to step outside their comfort zone,” he says. “I don’t like the sea, I don’t like cold water. But the reason I do this is because it sets me outside my comfort zone.” Challenging yourself, he believes, develops mental resilience, although the sea swim element isn’t essential. People in landlocked areas have been in touch about setting up their own groups. It’s more about getting out of bed, and meeting others.

Win the Morning, Win the Day has connected people at a time when many may have been missing contact with friends and family, and provided a space where the emphasis is on mental health and friendship, not physical fitness or tough challenges. Reeves makes it clear that nobody has to go into the sea if they don’t want to. “I have, and suffer from, poor mental health,” he says. “I know my triggers for that and I know how to look after myself. Some days are OK, some days are bad days, and that’s fine.”

Hearing about Scanlon’s group on that podcast “just triggered something and I thought: ‘I could do this.’ On that two-mile walk I’ve had deeper conversations with people I’ve never met before than with mates of 20, 30 years,” he says. “People have made friendships, some people have stopped drinking. Some people previously wouldn’t go out of the house, some people didn’t like groups. I am immensely proud, not of myself, but of everyone who has made it what it is. I’m not forcing people to be friendly, and to be nice and positive. That’s just what we’ve attracted.”

They are kind: when it’s clear that I have drastically underdressed for the weather, one member, Paul, lends me waterproofs. And by necessity, when you’re swimming outdoors in the dark, you have to look out for each other.

Meeting up early to exercise is hardly a new idea, but Win the Morning, Win the Day has a catchy name, a growing community (the Facebook group has more than 3,000 members) and an easily replicable format. Michelle Tucker set up her group in Surrey – they walk, then swim in the Thames – in October last year, after seeing Reeves on a BBC clip and getting in touch with him. “I think it’s the simplicity of it – bringing people together, meeting early, starting your day right,” she says. “People are open and honest, and share some really intimate things – they may be struggling with their mental health, with isolation, and they just talk to each other.” Or it’s simply fun and “a really liberating thing to do” to go swimming in the dark at 6am. “You kind of feel like a child again because you’re doing this funny activity. The inhibitions have gone out the window.”

There is a clear sense of accomplishment – it’s good to know you have done something healthy (the walk, the socialising, and evidence is growing for the benefits of immersion in cold water) before most people are out of bed – and the knowledge that whatever happens during the rest of the day, at least that has been achieved. But the emphasis seems to be on mental and physical wellbeing, not necessarily about optimising productivity and getting up early just to cram more into the day, which is what characterises so much early-morning fitness propaganda.

There are many books and large online communities devoted to the early-morning rituals of successful CEOs, politicians, artists and other high-achievers, with the implication that if only you could get up at 4am, similar success – or at least the ability to get a bit more done – would be within reach. But what if they get up early because they are CEOs, rather than that they became CEOs because they got up early?

Fiona Buckland, a leadership coach, observes that some of the “outwardly successful people” she works with have to be up early to deal with the amount of work that has to be done and “the early-start mantra is making a virtue of necessity. They are incredibly ambitious and are also under immense pressure from investors and shareholders to produce results, so stress can be a great motivator to find more hours in the day.” They also, she says, “tend to be attracted to extremes and risk-taking, rather than moderation and self-care, and some of the extreme early rising routines are more a symptom than a cause of their drive”. While we are encouraged to perceive such punishing regimes as disciplined and impressive, “the hidden underside is the high level of burnout, alcoholism, depression, mental illness, relationship breakdown, insomnia, high blood pressure and heart disease,” she says.

While Buckland is all for “optimising your performance, let’s include a few more ideas so that people have a wider range of options and practices, and can discover what works for them”. This may not include an early start. She advises finding out, by experimenting, when you are at your best to work on the projects that mean most. “For instance, I know when my peak times for good, flowing, creative thinking are and I protect this. It’s not 5am, especially in winter when it’s dark,” she says.

We each have a chronotype – loosely defined as a lark (a morning person), or owl (more alert during later hours), though few of us are 100% one or the other, and the balance can shift with age – and it would be “foolishness”, says Colin Espie, professor of sleep medicine at the Nuffield department of clinical neurosciences at Oxford University, to say to an owl type: “You should get up early and be productive then. It goes against their natural sleep-wake rhythms.”

The best way to have a good day isn’t necessarily to jump into the sea – or wake up at 2.30am then pray, work out, play golf and have “cryo chamber recovery” as the actor Mark Wahlberg does – but simply to get a good night’s sleep, says Espie. “That’s the primary fuel for alertness, concentration, productivity, emotional function, mental health and so many physical things such as immune function and cell regeneration. Ensure you get sufficient good-quality sleep, because even small amounts of sleep loss create difficulties for the brain, and with concentration, productivity and emotion.” Trying to go against your chronotype “will be more likely to be counterproductive. If [an owl type] forces themselves to get up early, they may find it difficult to go to bed earlier to get that sleep at the other end. Therefore, they will be running short on sleep, and that will do more harm than good in terms of emotional health and productivity.”

So don’t feel bad if you are not up to some 5.30am socialising and outdoor swimming – blame it on your chronotype. But I’m a lark, and – after being warmed by layers of dry clothing and quite a lot of smugness – I can see the appeal. For the rest of the day, I feel the memory of the chill of seawater on my skin, I am in a good mood, and it does feel as if I am “winning” at something, however intangible. Reeves says: “It’s not about affecting everyone, but that one message I get most days, that says: ‘I really needed that today.’ That’s my job done.”