I've got a step on one of my mig sets. Never used it. Nor the spot timer. Just use the trigger as zzr says. I suppose it could be done in theory if it was a 12v or 24v motor controller? Or you could be really flash and use a 555 timer circuit but I still dont see the advantage of having it.
The on time of the step or stich was variable from 60 to 80 per minute it was ideal for filling holes in thin metal it also had a spot setting and a shrinker setting which I never new what that was for. when it was selected it put heat into the welding tip but didn't work the feed wire.
The welder was a Tekker which is at least 30 year old and it was second hand then. I have a 160 and a 125. the 160 I have put a cheap Chinese speed control which seems to work as the wire feeds and there's a spark at the tip when touched to the earth clamp.
It must have been a thing on machines at that time? Mine's an eutectic / castoline which i bought off my mate. He's 55 now and it was the oldest welder in the workshop when he did his apprenticeship so it's probably the same age as yours. Its a function iv e never used but probably just personal preference.
Wouldn't you need something a bit more variable than a wiper relay to give you varying times? Don't know if you could put a potentiometer inline to do tgat? I'm sure an electronics guy will have a better idea about it.
I have an ESAB Compact 160amp mig that has a spot weld time timer and a stitch weld timer, I purchased this machine brand new 30+ years ago.
I've tried using the spot/stitch weld timer when I first aquired it, but found it took too long to set up correctly for old car body work, so just used the trigger timer method.
Some of the older flasher units use the resistance of the bulbs to set the time, if a bulb blows they flash faster.
I dont know if they flash slower if you added more resistance? Might be able to do something with one of those and a variable pot (or a few bulbs and switches)
Some of the newer stuff can have both the on and off times programmed over the canbus but you would probably need the whole body control module and the indicator stalk etc. to do it.
Step welding is quite usefull if you want to stick 2 sheets together at intervals, gives you a nice (cosmetically) even finish.
Nothing you can't do with the torch trigger and a bit of concentration though.