That oil pressure buzzer would only be on at start up for a couple of seconds
Yeah, I can't look at my bus quick enough to see oil pressure under 50 at startup (OK, that's a little bit of exageration, but I swear that the "groan" from the starter hasn't died away before it's up to 50). My bus is a 4-stroke, may be different from yours; I don't have a buzzer and I do have a gauge. What does drive me crazy is the air system buzzer (it takes a few seconds to build up enough air to switch off the warning horn) and I'd like a timer or whatever like you're talking about but it's an important safety thing. I guess the speed at which it goes off tells me something about how quick the bus is building air.
I have a "neutral" light on my bus. I wonder if I could rig a relay to turn off the air warning horn while it's in neutral?