You're growing in soil no? You want them to get bone dry before watering. Make sure to wait until the soil has pulled itself away from the edges of the bags so as to aerate the soil. No worries on forgetting for a day or 2 in soil. It may be dry on the surface but if the plant isn't showing signs of it being without water then it's not and that means the soil has a lot of water left in it. Drip lines don't usually work for soil but you could run a type of drip line that waters all of your plants. Place equalizers on the ends of the hoses so as to not run all the water into the first few plants on the line. Get the T's and use a pump and res. Should work out fine. You shouldn't have a timer for your water but rather a switch that you control. You can say when it's time to water instead of something that doesn't have eyes