Not sure how current this article is, but it can't have changed that much. Live is in the second part; main thing is you both have to be logged on to the live server at the same time. Just being logged on to chess.com isn't enough. Oh and congratulations on diamond. Sure you'll get lots of pleasure from it.
https://support.chess.com/customer/portal/articles/1444882
when i try to play a 10 minute against my friend, it sets me up with a 10 minute game against a random person