Reminders are scheduled work, and WordPress only runs scheduled work when someone visits the site. On a quiet site the reminder job can fire hours late, or not at all before the event starts.
First confirm the settings: Manifyst → Settings → Email → Send Reminder Emails on, Reminder Hours Before Event set to a sensible number (24 sends a day ahead), and the Event Reminder template Enabled. Reminders go to confirmed attendees only — waitlisted people don't get one.
Then confirm the schedule is actually running. Manifyst registers an hourly job named manifyst_send_reminders. A cron viewer plugin will show you whether it exists and when it last ran. If it is overdue by hours, WP-Cron isn't firing often enough.
The fix is to drive WordPress's scheduler from a real cron job instead of from site traffic. Most managed hosts offer this in their control panel: disable WP-Cron in wp-config.php with
define( 'DISABLE_WP_CRON', true );
and add a server cron entry that requests wp-cron.php every five to fifteen minutes. Your host's documentation will have the exact command.
Note that a reminder is sent once per signup. Someone who signs up after the reminder window has already passed won't receive one.
If no Manifyst email is arriving at all — confirmations included — the cause is delivery, not scheduling. See Signup confirmation emails aren't arriving.
