No it doesn't have its own breaks, the 20 min log is a failsafe that get triggered when you got stuck for 20 min.
Like when you dc or logout when you have ores on the belt.
It's impossible to keep track of it when you lose stuff all the time.
Either you can lower your breaks under 15 min or you can disable the option in the GUI.
Maybe I can rework this system now since the dwarfs work a lot faster then human tend to do in W358