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