Hi Lee,
I would say it depends and how much detail you want. I can spend as little as 2-3 hours if it's one color and nothing special.
The phantom was probably 60-80 hours. You don't see all of the detail and weathering. The panels lines for example took close to 10 hours. There are 4 shades of gray on the model. Had it been all grey it would have been a lot faster
When you do something like camouflage then it takes a lot of time too because you have to paint. Wait to dry. Mask. Paint again.
Personally I like the painting so it's not a problem. I also have acrylics, enamels and lacquers depending on what I paint