Normally if I have a dextro energy tablet, in about 20 minutes I start to speed up lots.
Unless it's the middle of the night....
I necked two dextro energies half way through a double lap at dusk til dawn last weekend. It would have been about 2.30am. For most of the lap I was half asleep, thinking 'any minute now, any minute now I'll wake up and speed up'... they kicked in in the last MILE after I'd spent a good 50 mins really struggling against the sleep deprivation and general exhaustion. B*stard!!!!