Continuing the discussion from Manage Locations:
@dougcutter & @njmike —
• Use Manage Schedules to create a new event like normal.
• You probably already know that the “Repeat how many times*” field will not accept a value less than or equal to 1, so, use 2.
• Tap “Save & Continue.”
• On the next screen the two instances of the new meeting you created will be displayed—each with a small, blue 
️ just to the left of its “Name.”
• Click the ️ to delete whichever instance you choose.
• Edit the remaining event, as needed, then click “Save Events.”
Now you have your one-time event🙂.
One thing to remember—If you need to edit this event, once you click “Save & Continue” the 2nd instance will be re-generated, so you’ll just have to delete it again.