Each meeting gets a fixed amount of time. It scrolls through the text at whatever rate will get it all shown during that meeting's allocation.
So meetings with very long agendas will scroll quickly.
In practice, I've found the meetings with really long agendas tend to have agendas that really do not convey any information (such as assessors standard agendas which don't tell you anything about they are going to talk about). So I've never heard any complaints about them flying by the the titles of a B-movie.
-Joshua