Water when your pot feels light. A very trusted way of learning how to tell the difference by pot weight for a new grower is take an empty pot the same size your plants are in, and pack it with dry soil. Put this plant-less, dry pot next to a freshly fed plant. In one hand, lift the watered pot with the plant. With the other hand, lift the empty pot.
Although the plant will add some weight, you should be able to get an idea what the dry and wet pots feel like. When the pots feel light enough to be near dry, water. Leave the dry pot in the tent to compare to the plants each time you check on them until you're perfectly familiar with identifying when to feed.
My veg plants in one gallon containers require feeding every three to four days. I transplant when I'm at the point I have to water them daily into three gallon pots. For a little bit, I have to feed them every three to four days. Eventually with the veg plants, and the flower plants also in three gallon pots, they all fall into a routine where I have to water or feed every second day. Clockwork.
If you go by the pot weight method, if you notice the plants wilting, you've waited a bit too long. Water/feed immediately. Over a little bit of time you'll get the hang of this method, and you'll very rarely over or under water in soil again.
