from my experiences a good luminaria ceremony should be no more than 30 minutes with the remaining 30 minutes of the hour dedicated to silent laps...this provides for both an engaging ceremony and personal reflection time...time will of course vary depending on the size of an event, number of luminaria purchased, other remembrance sales you might do (i.e. torches, letters, etc), and how luminaria names are presented if at all (i.e. scrolling powerpoint)