It depends of the training done in the weeks before the race etc, the 9am would have been perfect for me, I usually did my hardest workouts at that time. I once ran 15.51 doing 30x100m steep uphill at about 21seconds (~1500m workout) w/ jog down rec in about 45-50sec just 2 days before the race, and the day before a 45min easy run. Morning run in the race day and then raced in the evening on windy and cold summer conditions, leading the group behind me, and I kicked hard the last lap and my form was great, I fealt it and was told the same by other person after the race. I´m sure the hill workout was the reason behind this. Of course my time was weak but it was good for me, a PR at that time, main event was the 800m. The year after before my lifetime 5k PR (15:43 in perfect conditions), the day before the race I did 6x1k with 30sec rec at or slightly above the LT (~3:35 per km). I feel that often people taper too much for a race and feel empty and slow on the race day, OR then they feel great at the start of the race, but suddenly are full of lactate thinking to drop of the race. Been there, done that.
If you feel flat and empty when warming up for the race, I would suggest trying more agressive warm up, unless you´re depleted of glycogen and the race isn´t a marathon. This could give the pop back in your legs. I once felt dead before a 9k road race but I just jogged about 15min, didn´t force it, changed racing clothes and flats, and suddenly did feel strong right at my opening strides (3-5x100m) and felt great on the race too. If I would´ve still felt dead on the strides before the race, I would´ve tried some faster, preferably uphill strides to wake up the neuromuscular and cardiovascular system. After this ~10minutes of easy jogging and walking before the start.