does the wounded area appear to be oozing pinkish fluid? is it puffy around the wound or does it appear as if there are pockets of fluid close to or around it? those are signs of infection, which can go systemic quickly. a systemic infection is serious and can be fatal if not treated asap by a qualified vet (and even then, the snake might not be able to pull through).

The care of this animal is your responsibility, regardless of the weather or any other factor. do whatever it takes to get your snake to the vet first thing tomorrow. in the mean time, remove the rocks and anything with rough edges, do not soak the snake and use the triple antibiotic ointment on his belly and back (apply gently!).