Players could buy a button or switch from an economised shop.
This is not my recommended method but just showing it is an example.
It requires making edit zones, edit permissions & economised shops.
This is probably the most difficult method to initially set up but works effectively & requires no maintenance once done.
-Make a small edit-zone so players with edit perms can put their button in place.
-The button will be used to power a script to set the power on & off, allowing access for adjustable lengths of time.
-Make the script also remove the button so players have to buy a button each use.
1: Will clear the button away
2: Will set the power on for the safe to open
3: Optional/adjustable delay.
4: Turns power to the safe off. An optional & adjustable time limit can be put in place
-A 5th command line could be added to restock the safe after each use.