It will be fine as long as it's just a small leak that is leaving residue on the shaft. Just tackle the problem when you get home. I have seen guys ride with serious leaks, but I don't recommend it.
If you are seeing a leak that is running down the fork and onto the wheel while the bike is sitting overnight without being ridden, you have a major issue that needs to be resolved.
You do want to get it repaired as soon as possible though. Otherwise you could end up getting dirt in the seal. That would lead to scratches and a major leak.