The guys in the shop here made a mold of a welding helmet so we could build a few custom carbon helmets for fun. Building your own allows you to put any type of viewing window and filters you preferred or wanted by adding a flange to mount that specific manufactures window/lens assy. You can mix and match any manufactures stuff and build exactly what you want - then paint flames and skulls on it ...
We took a helmet and made a mold from that. (The red stuff is a surface coating) Then using the mold we made a couple helmets. Once trimmed and painted – we drilled out the headband attachment holes and added an adjustable headband. Building the window flange right now to attach the auto-darkening assy that just clips into the mount flange once we bond the flange to the helmet.
3 days. You're only limited by the cure cycles on the resins. You can place the mold or part in an elevated temp environment and accelerate the cure if you want - but there are limits. (we have a 120 degree hot room and also a couple big ovens if we need them)
1 day to surface coat and wet layup the mold off the original helmet. Cure over night.
The next day minor body work to the mold and then release the mold in prep to pull the part.
Third day layup the part and cure it over night.
Most resin are cured enough to work within 24 hours. It may take 7 - 10 days to achive full cure and strength properties.