I checked on my cowl repairs last night, so after a 24 hour cure it is rock hard. Quite pleased since these cans have sat on my shelf for at least a year or more since the last time I used them, with the pumps still in them. If anything, the shelf life seems pretty good with WS, and ease of use is right there too. One thing I do after slopping it on and satisfied with the outcome is hit it with my heat gun, the one used for stripping paint, and get it nice and hot, brush back any runs and drips and then once cooled, let it set. I do this for making molds and repairs, but not when making parts, I want that flexibility for removing the parts from the mold, then letting it harden slowly. I found that doing this also helps when putting the cowl on the plane, if its too stiff it can crack or craze.
It all depends on its use.