There is no point in giving examples on the second question, because for most truly groundbreaking results this time is really short.
On the first question, one can mention almost all results of Archimedes and Apollonius, which had almost no development in antiquity, and during the middle age there were no people who understood them. (People read and discussed more elementary books of Euclid, but not Archnimedes or Apollonius). True recognition only came in 16th century.
In the modern times, the period is smaller. One can mention Sharkovskii's theorem (see Wikipedia) which was proved in 1964, but was not noticed by the large mathematics community until the paper by Li and Yorke (1975) who proved a special case. This special case created a lot of excitement.
Another example is Fatou-Julia theory of iteration of rational functions
created around 1920. It was dormant and almost forgotten until new developments made it one of the most fashionable areas of mathematics in the middle 1980s.