Water when they need it

It's very difficult to say how often that will be because it depends so much on your conditions, soil, light, plants, etc.
In peat, it will probably not be every day. I have mine in plastic pots watered (lightly!) from the bottom and I put a little water in most mornings, but still sometimes they haven't finished taking up yesterday's water so I don't give them any more.
Watering is the trickiest part for baby seedlings. They can't be allowed to get completely dry or they die, but they are very sensitive to over-watering. You are trying to keep them consistently just damp. If you press lightly on the soil and water oozes up, that is too wet. After awhile, you will get used to what your soil looks and feels like when it is starting to get dry.