they regenerate at a constant rate depending on your server speed
RT gets 1 turn every 8 seconds, for example
however, each server has different turn Storages, which are the maximum turns you can hold at any one time
so if you are maxed out on turns you wont get anymore until you spend another turn
so, if you have the maximum number of turns, then use them, and you can get more
if you are at 0 turns, just wait, they will come back