User blog comment:Gearslover01/The number of time you leave the Animus in AC: Brotherhood?/@comment-4055238-20120909074216

First off, they're called Sequences from AC2 on. In ACB, you can leave the Animus anytime after the first Sequence and before the end of the last one. There are 9 Sequences in ACB. The notification will pop up every so often. I can't be for sure which memories, but I know the first one pops up after Who's Got Mail?.