Maybe I shouldn't have written "average" then, perhaps we can get an impression. And I am not sure if it depends on the programming languages you already know - maybe it mostly depends on knowing at least one language? I know it is all very fuzzy, for example what does it mean to know Java - surely not to know all available libraries by heart. But maybe people here can give an intuitive answer to the question?
My own estimate would be about a week (I can program after a few hours of course, but not with as much confidence as after a week).
Even if you took the average I don't know if it would lead to a useful statistic.