carbing keg over 3 days

I normally carb an already cold keg (32F) over about 24 hours at 30 psi and it does the trick for me. I kegged a beer last night but will be gone until Sunday. Any ideas on what pressure I should keep it at to get it carbed by Sunday afternoon/evening? I have it set at 20 psi as a guess.

Fridge is at 38F

24psi for 48hrs at ~38F generally gets me to 85% carbonation.  I think an extra 24 hrs would put me slightly overcarbed.  Perhaps 20psi for 72hrs would get you to ~85-90% carbed.  I don’t think you’d be overcarbed but you may still need another 12-24 hours to finish getting up to perfect carb level.  At least from my experience this is how I’d approach it.

Before I started spunding, I’d quick carb @ 30 psi/48 hrs/38F-ish for most beers, then reduce to serving pressure. Generally came out right.

Any guess for 72 hours?

I’d guess around 20ish psi for 3 days (since you’ll be gone) would be pretty close.

+1, 20-25 and you should come pretty close, no risk of seriously overcarbonating in my experience.