I think this could work well for some, and not so well for others. Some Yojimbo are particularly interested in certain areas, and particularly annoyed with others. Also, some people prefer to put in all their time in one or two chunks, then enjoy the rest of the convention freely. That's what I did with Sakuracon. I worked from Midnight Saturday to 6pm Saturday with a 2-hour break early in the shift. It worked really well for me because I had things I wanted to do Saturday night and all day Friday, but nothing in between.
That in mind, it's simply a matter of effective scheduling. 4 weeks before the con, the Yojimbo manager (all the managers should do this, actually) asks all their staff to fill in a time table marking half-hour slots as "preferred", "available", "off" (but not necessarily unavailable), and "unavailable". There should also be a table for which areas people wish to or not to work in, and each area could then be marked "preferred", "okay", and "avoid". Again, every subdepartmental manager should do this if they want to have the happiest, most effective staff. As more staff come after the initial schedules are made, they can be used to reinforce thin points in the schedule, fill in the blanks, and fill in to give the staff that got their stuff in early some bonus time off. Doing this would also give the managers a clear idea of exactly how many staff they WANT and how many staff they NEED, which they can announce at the final general meeting before the con.