My first iteration of a timed lock by an ice cube. The lock contains 3 parts and takes a regular ice cube. There is no need to put the lock in the freezer and worry about the parts breaking because of the expanding ice.
Maximum size of the ice cube this lock can take 30x30x30mm. It takes about 2 hours at 22°C for the lock to release.
To use it, put the two bodies together and place an ice cube inside. Place the lid onto the top and wait for the ice to melt. The lid snaps into the body with a snap fit and is slightly recessed so it's impossible to remove without tools. When the ice has melted and the 'key' part is removed, the lid falls out because it is held in place by the key part.
50% main body and lid, 75% for the key body
For strength, the parts have to be printed as the appear in the rendered pictures.
The main body (red) and the matching key body (yellow) have to be printed flat with lots of supports, and the lid (green) has to be printed upright. I have printed the lid on a raft for stability during printing.
I tried printing the lid flat, but the snap fit tabs broke off on the first try. The upright print still works fine and seems pretty strong.
For the key body I used 75% infill, because there is less material thickness compared to the main body.