I worked for a race car chassis builder as a fabricator for 8 years. One of my jobs was to make flat carbon fiber sheets for building race car interiors. This was done using vinyl ester resin and MEK as the hardener. These sheets were about .030 thick and were 5'x10'. Yes, that's feet! Used a sheet of 1/4" 5'x10' glass for the "mold". Because of the size, didn't have much time to lay up. Anyway, the resin mix was 3/8 oz. of MEK to 1 quart of resin, which would give about 25 or 30 min. working time and each sheet took about 4 quarts total. One time the weather here was cooler than usual, and this sheet was not getting tacky on the back like it usually did after 30 minutes. Because the table the glass was on, had wheels to move it around, we pushed the table out into the sun to speed up the cure rate. Bad, really bad, it cured alright, and cracked the $400.00 sheet of glass, and the carbon sheet was stuck to the broken glass for good. So, we were out the glass, and the $1,000.00 sheet of carbon. Come to find out the supplier shipped us MEK that was a higher percentage than the usual stuff had. We never did find the reason the sheet wasn't curing at first, though, but did find that little extra heat from the sun attacked the 4 coats of mold release wax on the glass. I don't remember what the percentage difference was, but it wasn't much. Any fiberglass resin, whether vinyl ester or epoxy based, is extremely sensitive to mix ratios. I don't see how, with small mixes like 4 or 6 ounces of resin could a person accurately measure the MEK needed.
I do remember that the MEK, when we would get close to the bottom of the gallon, the cure time was longer, but we always used the same ratios. I guess the MEK got weaker from age.
I would be real careful in glassing a plane, I would use only new, unopened resin and hardener. I saw a lot of weird things happen in fiberglass work.