It keep resetting the timer

Low Priority Queue works like this,

Its a pre-pre-lobby that doesn't count towards actual queue time to look for a game,for example, If you have 20 minute low priority, after that is done, you still have to wait another 3 - 5 minutes to search for a game,

and you can't leave, if you do leave either during low priority OR during queue time for game, the timer restarts. Pretty inconvenient but it is a punishment so its not supposed to be fun.

My advice would be to leave the timer up and viewable while you tab out and occupy your time with something else while you wait for your afk check.