I first tried the premixed form.
I rolled it into a ball and found it to be quite dry.
Pressing it on the feet, then putting the boy into it, only filled the crevices with the putty. Nothing really stuck. After about 2 hours the putty just wiped off.

Interestingly enough, the ball I formed, I noticed later, made a very nice clapper, rather like the lead ones in some of my bells. So it does harden, just didn’t stick very well.