I think it is shortening.
Jules Verne to the moonshot about a hundred years.
Arthur C Clarke described something like today's smartphones in the 60s and they arrived maybe 50 years later.
Right now extrapolations from today are, if it is a good idea, likely to arrive in 20 years ( three do printers creating Burger and Fries) .
Something radically new, if it is possible, will take maybe 100 years.
So the short answer is it depends: on how easy it is to develop the required technologies and how long before there is a demand.