They're pretty hardy snakes. He'll most likely be ok to wait one more day to see a vet. But I would definitely schedule a visit asap.

In the meantime, bump the temps up a few degrees, as you already mentioned...and make his enclosure as dark and secure as possible. Don't mess with him or do anything to add to his stress levels unless it's something essential.

You said "all the classic symptoms" but without detailed descriptions, it's impossible to guess how far along or how bad he really is. I haven't personally had to deal with an RI, so I can't give a personal story....but I wish you all the best with him!