This question can't really have an accurate answer. Times on 3x3 and times on bigcubes aren't directly related; it all depends on how much you've practiced each size cube. As a very nice example, Yuxuibbs says she averages 12 on 3x3 and gets around 4 minutes on his 2-5 relays. I average high 12's on 3x3, and the last 2-5 relay I did was 2:24, and that wasn't even a very good time for me. (EDIT: Just tried another relay and got 2:14 lol)