Sessions plans a MimicTyper run as several real sittings with real gaps in between, like sleep, class, or dinner, instead of one long unbroken block of typing, and estimates how many sittings a piece of writing would realistically take.
A session run survives interruptions: it reconstructs its caret position after a tab reload, schedules its own wake-up with Chrome's alarm system so the next sitting starts on time with the popup closed, and picks back up exactly where it left off after a browser restart.