If we were freed from the needs of a specific schedule, we would take this as signals of when your body wants to wake up and follow a polyphasic sleep schedule. If you're waking up at 3AM all the time, that's a signal your body wants to get up. If you're comfortable sleeping at 7AM, that's a signal that your body wants to sleep. So you would wake up at 3AM and do something for a few hours, then go back to sleep. Overall sleep time ends up the same, though there are some polyphasic schedules out there where you can theoretically sleep as little as 2 hours a day. They are extremely regimented on the schedule.
But good luck doing any of that while having a regular job.