Time delay dpdt relay using only pot, relay, and cap (discreet components and no transistors)
I'd say forget it. There is a reason all those circuits you see use a 555. A practical capacitor does not old enough energy to power a normal relay for the period of time you are aiming at.

You might get it to work with a very very low current relay, maybe a 230V relay, with an idem capacitor. But that is exactly the circuit you don't want a novice to play with. (At least, if you want him to live long enough to rise above that level.)