I understand you're aiming to apply for this round but do you think you can get to know this person in the next 6 days? At least enough to trust and believe in them (and their capabilities)? I think I remember reading something from PG a while back that talked about how team dynamics were pretty important and I know I've personally seen businesses torn apart because of cofounder problems.

I guess it is possible but just make sure there is at least some team chemistry and that you guys are compatible, since if you get into YC you'll be living together for at least 3 months. Best of luck!