I'm a female short sprinter, so I honestly can't speak to your times, but I'm thinking you're going to need to run a solid sub 50 to be competitive on the 400. I was contacted by UW in high school, so I don't know much about joining at this point - but I do know of a few people who joined mid-college, all of whom ran with the club team and joined the team after that. I would say getting involved with the club team is definitely your best place to start. It can't hurt to email your event coaches or the recruiters with your times and intentions. For what it's worth, I ultimately chose to not run because I realized just how much time it was going to chew up out of my schedule. I had offers from Yale and Johns Hopkins as well, but I also felt that there wasn't going to be a great school/sports balance at either school (ultimately an academic full ride here is what made my choice easy). To me, track wasn't something I was going to do the rest of my life, and I didn't want to risk putting academics at risk because I knew I would have rigorous classes to prep for grad school. I really think it varies from person to person - sometimes I was really disappointed I didn't run, other days I said thank god I didn't because I had so much more time and flexibility.