I made a small animation to show the unlocking mechanism more in detail.
It was one of the delicate points of this project, since it was necessary to find a purely mechanical system which unlocks the box at the moment it's empty so that it can be filled, not before, and just with the strength of the timer.
The problem with this mechanism is that in case of a breakdown, the box remains locked forever. It was therefore necessary to add an alternative way of opening it.
I tried with a mailbox lock but it was really too easy to pick it, so yes, I know I said there would be no electronics in this project, but eventually there will be a little bit.