What ever your feeding schedule is will determine how long they can go with out water. i would water them before u change the res. so u have some time to get things mixed and ready for the next watering. I use drip every 3 hours for 15mins. But the bigger the plants get i will cut down on off time. It shouldnt take more then an hour to dump ur res clean it and get it refilled and mixed. Personally i would flush the roots get clean water and dump it at the base of every plant to wash out build up, and then start the process. Once ur done hit the timer on. mine take about 4-5 hours to dry up, but the bigger the faster. Don't make it harder then it is, just do it. :jointsmile: