I have punted in the morning & the afternoon, with 12-2pm being my favourite start time, as it gives me time to travel there & back & still enjoy my evenings doing something else.
Saying that, I will have to try an evening one sometime just to see if it gives a different vibe, although if the SP has been busy during the day it could have an adverse effect.
The only day I haven't punted on is a Sunday, but from what I seen most SP's don't work that day anyway.