Floyd Mayweather is facing 90 days in jail, and he'll surrender to the police on January 6th. So if he serves the full 90 days (I'm not sure how good behavior works in Nevada) he'll be out in early April. So, the proposed May 5th date with Manny Pacquiao will almost assuredly be cancelled.
Assuming Floyd is out by April, you would have to think the Manny Pacquiao fight would be pushed back until at least July, if not later. Floyd would probably need some time to get acclimated before anything at all. Then there would be time needed for promotion of the fight, before the fighters finally get into camp to train. While they could probably do the promotion at the same time as the fighters training camps, it would still force the fight to be postponed until later in the year.
I really hope that the Mayweather-Pacquiao fight, if a deal is made, could happen sometime in July. That is typically the latest part of the summer in which major fights occur, as August usually is a very slow month for boxing. Realistically, if a deal is struck, I expect the fight to take place sometime between late September and mid November.
This time frame would allow for plenty of time for Floyd to get into shape after he gets out, give ample time to promote the fight, and give the fighters time to have full training camps. Something no one is really asking though is how will Mayweather's jail sentence affect Manny Pacquiao?
I think Floyd going to jail will have both a positive and negative impact on Manny. First, anything that could possibly derail Floyd's routine of always staying in shape and being in the gym will be to Pacquiao's advantage. He'll be able to train while Floyd sits in a jail cell unlikely to be doing much boxing related activity.
However, one thing that I think hurts Manny is that he'll probably have to have another fight in the early part of next year, as Bob Arum and Top Rank won't want to keep him on the shelf for almost a year if he fights Floyd in late 2012. If he fights Marquez for a fourth time, he seriously risks losing, and also it'll be a difficult, taxing fight; something he really doesn't need to put himself through before what will be the toughest fight of his career.
I expect Manny to fight someone who is a solid B+ level fighter, who will keep him active but won't put him at serious risk. Basically, Manny will probably have a stay busy fight sometime between March and May, which is when he's traditionally fought.
Mayweather's jail sentence will without a doubt impact both himself and Manny Pacquiao. Hopefully once Floyd is out, he can finally rid himself of the legal distractions, and strike a deal with Manny Pacquiao and give sports fans the fight they've been waiting for.