The humidity is probably not the problem. What temperature range have the joints been subjected to?

I don't think you'll have a problem if you scrape the unhardened 'glass and epoxy off, clean the area with acetone, and sand lightly before your second attempt.

If even the unused epoxy in the cup hasn't started to harden after 24 hours there is most likely a mixing problem. Why don't you mix up a small batch as a test to make sure you have the ratio right and also that you don't have a bad batch of hardener or resin. I assume that System-3 has several different formulations. Which one are you using?