Ice Lock ++ by trapfox on Thingiverse: https://www.thingiverse.com/thing:2640495

Summary:
Slightly improved Ice-based timed lock.  Compared to the original this one has internal expansion ribs to reduce strain as the water freezes.  A thicker key with external ribs to hold the ice better.  Reduced overhangs and no bridges for easier printing.  A flat-bottomed internal cavity to reduce leaks from slicer-created geometry.  Freeze the pin in the body, and at room temperature, it will take 2-3 hours for the ice to melt enough to release the pin. It's a nice alternative to cobbling together an electromechanical timed lock, and more reliable as you're not in a freezer :P