its not the matter of how much fluid moving around in there. cause its not really moving around in the lines and calipers. its all about preassure. and thats the same. the ABS ece do not "know" in advance how long it should so its stuff. it gets signals from the abs sensors at the wheels that they are rotating again. therfore it can alow braking again. this goes in cycles. it dont know anything it just reacts on what the wheel sensors are telling it