at our plasma center, they dont give you cash anymore, they give you a card and put the money on it, if you lose the card YOU have to pay the money for a new one. i liked it better when they gave you some cash.
i've never given plasma myself, but i know several people that do regularly (i used to work next door to the local plasma center) and they all said it takes anywhere from 20-45 minutes to donate. of course, there's still a 2-4 hour wait to even start. and whoever mentioned going after a meeting, i know at ours you need to be in by 2 or 3 because they close at 5 and don't want to be stuck there later, so that would probably only work for an early meeting