problem that the roots are in the solution for 15 minutes

[HAWK]

Ron you are the best hydro site on the net. now that i softened you up i have a couple of questions. regarding the 11 plant system i read that for my "tomato" plants i should water 15 on and 15 off. only problem is that the roots are in the solution for 15 minutes as the timers shortest increment is 15 minutes. the bottle fills up in 2 or 3 minutes. all that extra time the roots are submerged. is it ok to leave 15 on 15 off? also any ideas as how to convert the 2 litre to the 1 gallon size. thanks again HAWK