How long did Tavros actually know Jade before confessing to her?

A few hours. Jack arrives to the Troll Session 10 hours prior to him destroying the Genesis Frog, and Tavros goes to stop Vriska 3 hours prior to the Critical Event. Furthermore, he’s asleep for a while and has his robo-legs implanted, which means at most, if he literally spent every other waking moment he wasn’t chatting with anyone else, watching her life unfold, I’d say about… 5-6 hours?