If I could, I'd punt at the start of the day when I'm fresh and not tired or stressed from work. Also, there are studies saying a man's libido is highest in the morning. However, punting in the morning is not the easiest to organize and many WGs don't start until close to lunchtime.
I've had some great punts in the evening and some terrible ones so it's impossible to generalize. A lot depends on your daily habits, whether you are a night owl, and the type of person you are seeing. If they are taking multiple bookings and crowding them together, then it makes sense to book early in the day.