The two kinds of follow-up
Once someone registers, two different things keep the session alive for them. The first is the product: a confirmation email landing in their inbox with their private access link, an .ics calendar file and a Google Calendar link inside it, then automatic reminder emails at 24 hours, one hour and fifteen minutes before the start. You set none of those timings individually; they run unless you switch the reminders off.
The second kind is anything you write yourself. A pre-work note, a bring-one-question line, the slides pack afterwards โ messages from a named person that add something the schedule cannot. The honest way to read this page: the machinery handles attendance logistics, and you handle the part that makes a session feel worth attending.