Researchers found 'temporally consistent exercisers' work out for longer - regardless of if they went in the morning, afternoon or evening.
A study of 375 adults found those who had a routine worked out for an average of 4.8 days a week and a total of 350 minutes.
This is compared to 4.4 days and 285 minutes among the 'temporally inconsistent exercisers'.
The scientists believe working out at the same time helps exercise become a habit that people automatically set aside time for.
Despite exercise's benefits, many struggle to meet the recommended guidelines for physical activity, the researchers said.
Two-and-a-half hours of moderate-to-vigorous physical activity a week is required to 'improve health', the team wrote.
And the experts at The Miriam Hospital, Rhode Island, said at least 250 minutes is needed for 'long-term weight loss maintenance'.
Studies have shown people who manage to keep the pounds off tend to be better at sticking to strict diet and exercise regimens.
Previous studies that have delved into the importance of timing when it comes to exercise have thrown up mixed results.
One found women who work out in the morning are less at risk of obesity. Morning exercise has also been linked to better fitness before weight-loss surgery.
To better understand the link, the researchers led by Dr Leah Schumacher analysed data from 375 people.
They used figures from the National Weight Control Registry was set up to establish the behaviours of 'successful weight-loss maintainers'.
Of the participants, 255 were classed as 'temporally consistent exercisers' because they tended to work out at the same time over a typical week.
Results published in the medical journal Obesity revealed those who stuck to a 'set' work out time exercised more.
Of the temporally consistent exercisers, 86.3 per cent met the recommended 150 minutes of physical activity a week.
This was compared to 74.3 per cent of the 120 inconsistent participants.
Repeatedly exercising at the same time may create 'cues' that help to establish habits, the researchers wrote.
For example, if a person consistently goes to the gym after they leave the office, they may start to associate the end of the working day with exercise.
Once something becomes a habit, the 'attention, effort and motivation' required to perform it gets reduced, the researchers wrote.
Nearly half of the consistent exercisers worked out in the early morning - they managed around 357.5 minutes of exercise a week.
This is compared to 319 minutes among those who worked out late morning, 330 among afternoon exercisers and 355 for those active in the evening.
Although the morning exercisers spent longer working out, the differences between the other groups were not found to be significant.
Exercise levels was not influenced by where a participant exercised, the type of work out they did or the mood they were in when they did it.
The researchers stress future studies should analyse how exercise cues become habits over time.
Study author Dr Dale Bond said: 'Our findings warrant future research to determine whether promoting consistency in the time of day that physical activity is performed can help individuals achieve and sustain higher levels of physical activity.'
Dr Schumacher added: 'It will also be important to determine whether there is a specific time of day that is more advantageous for individuals who have initial low physical activity levels to develop a physical activity habit.'
The Daily Mail
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