I received a request for an Event quick action to default to 15 minutes instead of the default hour. I stumbled upon this 7 year old SF idea and figures it’s not possible.
I made my client a new custom quick action, made a new custom field on Activities called ‘Duration in minutes’ and placed it on the quick action layout and removed the End Time field from the layout. I set my custom Duration field’s default value to ’15’ and upon trying to save the Event record, got hit with an error saying that the field DurationInMinutes cannot be null. That’s a standard field on Event which cannot be placed on the quick action layout.
I’ve been dabbling a lot with the new features in Summer ’20 and decided to give a before-save flow a shot to see if I could set that standard field which can’t be placed on the layout to be set with the value put in my custom field. Turns out it’s possible and it works.