There are sequences, targets and events.
A sequence can have several targets and each target has several events (unique combo of filter, exposure, binning etc)
You can have set start stop times for each target, or an overall one for the sequence. Generally my sequences only have one event, so it does not make any difference. When I'm chasing a subject and it is already in the west when I start imaging, I'll image that one first and then stop that target and start the next, using the times, when it gets close to my imaging horizon.