What time of day are Scheduled Reminder Event Emails sent?
This varies but is configurable.
If you go to Administer menu &gt; System Settings &gt; Scheduled Jobs you'll see a job called Send Scheduled Reminders.  It will also say what time the job was last run.  It will run 24 hours from the last time it was run.
You can edit the job to force it to run next at a given time. It will then run 24 hours from when it was previously run.
A good improvement would be to allow specifying a time, which should be possible these days - CiviCRM stores a time internally to deal with timezone issues.  This would be especially helpful for users who have modified the scheduled job I mentioned above to run more frequently than daily.