Help needed! Wound on rat!!

(I have two rats, Peaches and Dotty)

I've just gone to bed and fed my girlies, I shut the cage and Peaches came up to the bars with Dotty and then seemed to sneeze violently. She kept doing this with a very pained sort of forced squeak so I got her out with Dotty and put them on the bed. Peachy continued making this noise for a bit and it eventually died off. I was thinking she might've had a blocked nose or something, so I just let them run for a bit.

It was then I noticed on Peaches' back, she has a rather large open wound. It's only torn her skin and there's no sign of bleeding, I'm just not sure what to do. I've bathed it with some salt water (as best I could, she kept trying to eat the cotton wool) and I'm now looking at savlon or germolene or something just to keep it from getting infected.

I'm planning to take her to open surgery at the vets tomorrow morning, but is it okay to leave it that long? It just looks very nasty and I don't want it to open up or anything.. She's happily running around otherwise and doesn't seem particularly bothered about it..