When you are at the event creation page, make sure that the event starting time equals the current time (both highlighted in yellow on the screenshot below). Also make sure the event is set for today, and not for yesterday or tomorrow. Then, make sure that there is a reminder set for this event, 10 minutes before the start of the event (highlighted in green). Then click the save button in the top right corner to save the event.
It will take the calendar app a second to actually save the event and update the database, but this is all done in the background. Calendar Snooze should pop up within a few minutes from saving the event.