They start off, and stay off until you act
A new workspace has no reminder times set at all. Nothing is queued and nothing goes out. This is the honest default — a reminder that surprises a family the day you sign up is worse than no reminder — but it does mean nobody is being reminded of anything until you say so.
The two conditions
First, you set how far ahead a reminder should go — the lead time. Until there is at least one, there is nothing for the system to act on.
Second, the deployment has to be running the scheduled job that actually sends them. That is an administrator's setting rather than yours, and it is the usual explanation when the times are set correctly and still nothing arrives. If reminders are configured and silent, that is the thing to ask about.
What a reminder still respects
A reminder is not a way around somebody's preferences. It passes through the same gate as everything else, so a family who has unsubscribed or turned that kind of message off does not get one, and your quiet hours still apply.
The Notifications screen is where you can see what was sent, what failed and what was deliberately withheld, with the reason attached to each.