Dear Vinny,
they usually did a crash dive in less than one minute. Anyway to come up to periscope depth took several minutes since they had to carefully re-trim the boat: if you go down in a hurry you don't wish to resurface too soon, do you?
"diving times" has been "deeply" debated on the Forums' sections; just paste those words in each search engine and you will be "flooded" with results.
:-) Greetings
walter M