Usually it is because I don’t like to get the notification at 8:00 am. Since the forum is about a hobby, this is not the time I spend most time there. So I would open the notification menu when I don’t have much time and then the notification bubble disappears, so it does not help for the evening.
I usually use later today (mostly when I’m on mobile, as a substitute for “when I’m back on desktop”) or tomorrow when I read something at the end of my day and I want to follow-up the next day. For everything that’s further into the future I usually select a custom date (the time is mostly an annoyance in that case).
i love bookmarks and use often. i only ever use (in order of frequency):
none needed
later today
custom date and time - specific to the bookmark subject
rather than rely on reminders (i find them a bit annoying personally), i just periodically go review my existing bookmarks and remove any that i don’t need or want anymore. i would probably use the reminders more if i had reasons to, like for reminding me of meetings or deadlines related to posts about projects or solutions for example, but i don’t generally have that with my forum, nor on Meta.