If you have the right mixture of hardener and resin, ideally, it should dry in about 20 minutes.
Personally I use 25 drops of hardener per 2 OZ of resin. And I usually have about 7-9 minutes to spread it around before it begins to goop up.
Point being, you can easily resin an entire helmet in just a few hours if you want to, but dont rush it, because it will turn out badly. My first helmet was sorta lopsided cause my dad and I did the entire outside in 10 minutes, so yeah....
Fiberglassing will take a bit longer, just cause you have to cut and fit, and such, but I guess, you could have a helmet resined and fiberglassed in one day. I cant, cause I have work from 8-5 =/