Hadn't been invented when this game came out.

Score zero points then drain...

I would replace the color gi bulbs with white LEDs. It will allow you to see the ball better and will make playing easier.

If no points are scored you shoot again. Some games are made so it's impossible to score no points. On future spa the only way to trigger 0 points is to hit the ball softly so it comes down through the spinner without registering a spin and drain down the middle.

As for x seconds minimum, we had an expression at Bally for last second feature requests, "hand him the disk!".

I dont own this game but own two other Ballys of similar era, if you think this through there is really no way the game could do this. It has no way of knowing when you plunge the ball.....

I dont think you can do this even with modification to add switches etc, without reprogramming the entire game- unless you built a small circuit that operated entirely independtly of the game and used some invented mechanical means of diverting a drain to feed the plunger and had a timer with a plunge detect. Otherwise your basically reprogramming and rewiring the enitre game to accomplish this. Forget about it!

Most games don't start the ball save until you validate the playfield, not based on plunge. It could easily be added to existing games with some minor rom hacking

Good point...

Now about that easy ROM hacking step...

At any rate- for the OP your answer was clear from the first response. Sorry- would be cool