I like to play 5-minutes games. I use Dasher and press “5” icon to be paired with opponents. All of such games are put in 5-minutes category. Time to time I use rematch to play again with the same opponent. But such games are categorized as blitz game. Could someone shed a light what is the the difference between 5-min and blitz?

Yes, of course. You cannot rematch a player in the 5-minute pool. In any of the pools, it’s the server that pairs you up (trying to find players whose rating is as close to yours as possible). This means that if you issue a rematch command after having played a 5-minute pool game, you’ll get a “normal” blitz 5 0 game. In other words, the moment you issue the rematch command, you are not in the pool, waiting for the server to pair you up. the 5-minute pool differs from “normal” 5 0 Blitz because of the following rules: no computers players are allowed in the pool; you can’t choose your opponent; any disconnection will count as a forfeit. These are the main reasons for the pool is considered “pure rating”.
Hope this helps.