Wellbutrin is really fast acting compared to other antidepressants. If you were really down, I think its totally possible to feel something on the first dose.

Risperadal worked like that for me. I was in a depression where I couldn't get out of bed and having wickedly racing, disorganized thoughts at the same time. Three hours after my first dose and I was a completely different person.

Starting Effexor I felt it pretty much right away, I would say by the second or third day.