So, imagine 747, how did you imagine the japanese characters?
Females, bunny ears, half naked (topless), 3 pairs of teats?
Come on, tell me the truth, how sick of a dirty imagination do you have?
Feel free to attach hand drawings or whatever
The first one is almost always the hardest and it can be from few days to few months, depending on gunsmithing experience, machining skils, shop capabilities, availability of parts and so on.
After making ten of them, you gain experience, know what works and what not, build confidence, so it should be around a week, if having all the parts and shop capabilities.