Hi Brenton,
This post slipped under the radar but better late than never
If you look at the graph of variations in performance (underneath the graph of the temperature cycle), you will see the performance stats are at their lowest in the period from 3-5am. Now, there will be variation amongst individuals but in general, that time is when most people are at their lowest ebb. It is no coincidence that most natural deaths occur in the early hours of the morning.
Between 10 pm and, say, 1 am, your temperature and performance levels are still relatively high so theoretically most will find it easier to stay awake.
You mentioned that you feel better in that period because you know the sun will soon be up. Perhaps your "good" feelings are mainly psychological and maybe they are also triggered by your rising body temperature and performance. Your rhythms have passed through the trough and are now heading back up towards alertness. Who knows? There is always room for individual variation. I for one feel totally shite at 3 in the morning
Anyway, as far as the question is concerned, from the answer options given, most people will find it hardest to stay awake between 3 and 5 am since that is when their temperature and performance are at their lowest.
It's all fascinating stuff.
Cheers,
Rich