Ice-based timed lock. 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 long as you're not in a freezer :P

Printed in Hatchbox PETG at 246C, the lock will support >100lbf with fresh ice inside. PLA also works well, but ABS prints have shattered from the expanding ice. If you have that problem, check out the similar design in the "remixes" section that improves on it.

If your print isn't watertight, try increasing the extrusion multiplier by ~15%. The intent is to print with the following settings: 0.5mm extrusion width, 2 wall outlines, 0.3mm layer height, I used 20% infill.