it depend on individual, but anatomically i believe at night u would have been stressed up, so u don't really enjoy it, in the morning, all the systems is fresh and ready for action, all the hormones are ready not tired. the most importan thing u need to do is to brush your mouth or take a shower if u are the type to be sucked or leaked. u are in a better position to experiment, do it at night and in the morning u will know the difference. i like sex at all time but i obtain best orgasm in the morning, my ex girl also like it best in the morning.