Where were you looking in the manual (and which version)? in the 3.5 version, there’s a table of durations for all popovers that need them (bars/beats, tempo, tuplets).
It’s not in the inputting task because we never describe the full list of popover entries there, it would disrupt the steps too much. However, all tasks should have a related link to their popover or panel (and indeed inputting bars/beats with the popover does).
Re: slowing down time to add a caesura, you want the Time track, and you may also want to change the height of tracks and also zoom horizontally.