No, solvent is really no indication.
The curing process for polyurethanes you buy as single component coatings actually undergo a secondary crosslinking reaction well after the solvent has evaporated. This is why the directions say to not wax for at least two weeks after applications. The reaction connects the urethane resin pieces to a very high molecular weight by a slow reation with air. Prior to this the resin is soluble. Two component systems utilize a hydrox component (alcohol functionality) which undergoes a co-polymerization with the isocyanate containing resin directly forming the high molecular weight coating which is fuel-proof. There are many purmutations of this. Epoxy coating are a completely different chemical reaction, but the endpoint is a high-molecular weight material (very big molecules) which do not dissolve.
Try this experiment at home. Spray out 5 small panels with a single component coating. Allow overnight curing of panel 1, see how easy it is to remove the coating with your fuel. Allow the 2nd panel two days and repeat the stripping test. Give the next double (4 days) the time. continue this trend. For added entertainment wax one panel after the first day and see how fuel proof it is after two weeks.
The test will be in 1 hour
Team MRC-Hirobo and Model Avionics Rep