I usually say "When was the last time...?", but I came across this conversation. So I wonder which one is correct: is, was or either.
Henry: I was on the phone for an hour.
Ron: Who were you talking to for an hour?
Henry: Sam, an old friend from college.
Ron: When is the last time you talked to him?
Henry: At college graduation!
Ron: Wow! That was 30 years ago!
Henry: We had a lot of catching up to do.