If depends on the reason. If it strongly irritates my skin then I'll wash it off and get rid of it immediately. If the reaction is milder then I might give it a few tries.
If I don't see any results, I'll keep trying for 1-2 weeks.
I'm very impatient so probably just one or two tries. I'm more patient with makeup than I am with skincare, which doesn't really make a whole lot of sense since it takes a while to see results from skincare, but that's just the way I am.