I'm with Dale. If the top of the soil is starting to look damp, they have had enough to drink.
When I am starting seeds, unless they are ultra hard to germinate (such as Brugmansia) I don't water them after the first time. I use plastic to-go trays, add about 1.5" of potting soil, plant the seeds and stick the tray in water until is so super saturated. The plastic lid goes on and it sit over a heat source. It takes the tray about 10-12 days before the soil starts getting dry and by then the seeds are normally up.
I think this is one reason my plants got so big this year - instead of taking 2-3 weeks to pop through through ground, it was a week or less. Plus they had larger roots and once I transplanted them into pots, they were able to grow a lot faster.
Mike