Well depends on your exercise regime for the week, your work and other daily activities, you diet, your genetics etc etc.
I've cut out all cardio the last month or so as I've been studying for exams. So I've just been hitting up the weights 3 times a week. Got a good routine, good supplements and good diet.
And like my above post says, I'm working out after work, so its a good time of day, i really push myself in the gym, but don't over do it. Restricted number of exercises, but i push the weights/reps/rest times. Good supps to give my body what it needs for optimal gains and then an hour or so later I'm eating dinner - by the time this is processed in my body, I'm resting or sleeping so the benefits or rest are setting in also.