Watering is subjective. The simplest way to decide when to water is to water the plant enough so that you have just a little bit of run through coming out of the drainage holes on the side/bottom of the pot, then pick the pot up and see how heavy it feels. Wait several days until the pot is really dry and your plants are just starting to look like they are starting to wilt a little from lack of water, and pick up the pot again and test its weight. Water it like before, and from then on give it more water when its about 2/3 of the way between wet and dry weight.
Your other option is to just take some time and learn to read your plants. During vegging young plants can go longer without watering, so sometimes your only watering twice a week. However, those same plants may want to be watered every day once your into week 7 of flowering and they are 4 foot tall. The size of the pots also matters, as does the intensity of the lights. You put a 3 gallon pot under a 400w HID and it's going to need watering every 2 days, where a 5 gallon under the same light would last 3. They will also go through more water the hotter it gets, so if your like me and have trouble keeping your grow rooms temps under 80 they are going to need it more often. The good news is that it really doesn't take long to read your plants if you pay attention, and by the end of the first month you should be done second guessing yourself when it comes to watering. Just remember that less is more when you are first starting out, and go easy. If you underwater your plants you can usually recover from it easily, but overwatering them when they are young can easily kill them.