It would depend on the breed to maybe say what's wrong. My small breed get snuffly when they start to teeth and their nostrels become pinched, which makes it hard to assess if the nose is breed correct.
I think as long as the fluid is clear they should be ok. A lot of vet with my breed and similar tell you they have an infection when you take them for jabs.
If you think its an infection. don't wait until Friday, maybe bring the whole visit forward if worried.