Cockerels usually want to start mating a pullet just before she's ready to lay, so chances are her first eggs will be fertile. You'll never know, though, as it takes quite the practiced eye to tell if an egg is fertilized or not. No difference in taste, smell, etc. It takes several days of an egg being around a hundred degrees for an embryo to start developing, so if you simply collect your eggs every day or even every other day you'll be fine. I've had roosters with my layer flock for 20 years and not once have I cracked an egg to a partially developed chick.