Yes, you wouldn't want a manual dashpot switch to replace a dashpot relay. *ALL* the momentary switches would need to be replaced with dashpot switches vs simply replacing the time delay relay. Nowadays an electronic time delay relay would be the best choice, but that would need both Line and Neutral from the panel to power the time delay circuit. As there are only three wires, and two of them must be to the momentary switches and the load (lights), you cant simply drop in a modern off delay relay. Assuming you cant find an exact equivalent, get an electrician to install a DIN mount electronic off delay timer in the panel . . .