Further to my posts 8, 9 & 11, I finally managed to code for myself a lock timer for (my rescue closet) doors. But my modded version of Silvers' plugin works to allow only members of my server to access the 'key' to LOCK or UNLOCK the timer-lock on the doors (the key is a special action ofc - by pressing the USE + CROUCH buttons). Doors can only be unlocked or locked again after each timer-lock has expired for each door. The default timer setting in the config file is set to 60 seconds - which is perfect for my needs.
Public players can only BREAK the lock on the door, but only after the lock's timer has expired. On my server, I won't allow the public to use the 'key'. Instead, public players have to first BREAK the door lock by aiming at the door (or its handle), while at the same time pressing the USE and FIRE buttons together, then the door can be opened. There are also in-game onscreen instructions for players explaining how to BREAK these door locks too.
My code may need some cleaning up - optimization perhaps - but if any other coder here wants to make any changes to it, be my guess to alter it.
EDIT: I've updated this script to also allow for dead players in spectate mode to unlock a door for themselves, instead of just relying on a public-player to just shoot the door lock off. Also updated the help text messages to be much clearer too.