I want to make a film of a puppet jumping in the air into the water of a lagoon. I am looking for a pad with a spring release timer that I can bury in the sand so it's out of sight from the camera, wait 10 seconds for example, and the spring or coil releases and throws the puppet in the air, making it look like the puppet jumping with its legs. The mechanism is similar to "jack-in-the-box" and all I can find is the fast-food restaurant. I have also found no relevant results with "spring with delay", "spring release with pad", and "spring release with timer".
What is the name of such a device?
Update: Here's a drawing for what I want to achieve:
I am looking for the name of the complete mechanism, including the pad for launching and the release timer.