How long will it take for my arm hair to return to normal after my cast has been removed? weeks or months or years? it's already been week

Months: It will probably take a couple months for the hair to return to "normal", roughly the same amount of time you had the cast on +/-2 wks.

Hard to say: It seems in my experience that this can be different for everyone. For some people, the hair returns to normal color and thickness/thinness within a couple of months, but I have also known patient to have the dark, coarse hair for many months afterwards. I think a week is definitely too early to be seeing dramatic results/changes, if any, but my best guess is months to a year or so.

Hair after cast: generally the skin and hair return to normal in several weeks following cast removal - remember for the last 6-8 weeks the skin hasn't had sunlight and has been kept in an artifically moist environment. I think things will return to normal in 2-4 weeks.