I think people should take as long as they want to finish their character sheets.

I also think that everyone else shouldn't need to wait for them. Those who can't finish their characters for whatever reason can jump into the RP when they are done. I have seen hella' many RPs die because the DM refused to start it, because they are waiting for 1-3 people, while 7-10 people are active daily, and forced to wait for those 1-3 people.