It can take a couple of weeks for bluegrass and fescue seed to germinate. Ryegrass normally germinates a bit faster. Unless you're watering enough to wash the seed away or if it's actually covered in water, you're probably not overwatering at the germination stage. Once the seed germinates, you'll want to cut back on the watering frequency, but until then it's important that the seed never dry out. For that reason, it's often recommended to use a light mulch of shredded straw on newly seeded areas. The straw holds in moisture and improves germination.