it might be just me but im not sure if i really under stand the question. what are you trying to use a timer 2 come on and off for? if its for your misters,some people do 15 min bursts and some people perfer to run them 24/7 . if this is your question and i was you, if your rez was in a seperate container i would run the sprayers 24/7 but since your doing a combo,your plants will allready be sitting in oxygen rich water and wouldnt be needed.however, if you have your pump set to turn of and on every 15 min for 24 hours your going to burn your pump out a lot faster than you would just letting it run continuesly.but if its a smaller grow you can pick up the aqua culter pumps made by hydro farm for verry little money at any hydroponics store.its one of the few products from my local company that is not a piece of crap,but i have about 10 of there pumps in different gpm's and i have never had one fail.