Q and I are, and always have been, fluid bonded. He was my first, we were committed/mono and he'd been tested and I didn't want my first time to be with a condom. We did non-PIV sexytimes for months beforehand though.
I've told him that if he and Miss M get to that point, I wouldn't mind if they became fluid bonded as long as she's tested. It's unlikely to happen since neither of them are fixed and hormones mess her up.
I still have no other experience, so can't comment there. Can't imagine it would be quick though.
Me: 30yo wife
Q: 29yo husband of 5 years
(The Divine) Miss M: 27yo mutual friend, GF of Q just recently