In the past, it varies. Ive had long term relationships and an engagement where jt took several "get to know you" dates before jt really clicked. But, my current girlfriend and soon to be fiance, within 10 minutes of meeting each other it was an instantaneous.

To be fair, mutual friends did the whole "you two would be perfect for each other" thing for months ans months and tried to push us to meet so we had a lot of "Intel" on each other before we met so we e both has an idea as to what we were getting into. When we did, it was a just kind of a mutual affirmation that we were insanely compatible and I almost instantly saw her as a long term partner.