This self-tightening method is based upon a one-way ratchet-like device and a heavy object to pull the slack out.
When the ice melts down the lock releases the SRD and the pull rope releasing you or creating enough slack to get to a knife to cut up the ropes.
Here's an example:
The time lock is attached to staircase bars. So it hangs between two floors.
A suitcase used as the weight and pull rope with a cinch noose
The trigger rope. It keeps the suitcase in "midair"
The loose end of the trigger rope is taped in an easy reachable place.
The pull, trigger and safety ropes and the weight.
The suitcase hanging on the safety rope.
The proof of concept is here.
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