I wouldn't use the second one at all, Bulenteren. The 'since' clause refers to a point in past time, a 'meeting' time.
It has been a long time since World War II ended.
It has been a long time since I ate lunch.
It has been a long time since we met.
Having said that only the first one is formally correct, I would guess
that many native speakers say either one without thinking too much
about the logic. I see no difference in the intended meanings.