In my area summertime traffic is rather relaxed without significantly expressed traffic spikes, so journey time is almost independent from departure time. This summer I had liberty to come to work at any (reasonable) time. I spent large part of this summer without an alarm clock (had one safeguard alarm that always fired at work or during commute).
If I wanted to stay late, I could. I just went to bed when I felt sleepy. I would wake up naturally at varying times. Interestingly, I think I had one of the most productive periods, I felt well rested even though my sleeping pattern was greatly messed up. Waking up at 4am for 3 hour trip to work was not torture. had to do the same last week and was literally a zombie.
Furthermore I am one those people who occasionally wake up at night. I could keep laying in bed for those 15 minutes or I can check something (idle miner, bullshit feed) on my phone and crash after 15 minutes. Such options really depend on the person, I guess.