I am sure you will get lots of responses to this. I have always done my first fertilization in late February/early March, my second in June, third in August and fourth in October. Many say you don't need to do the fertilization in August but I think it really helps my lawn. This schedule is what I follow for fertilizing. If you use corn gluten meal as a pre-emergent, that may change your schedule a bit since you get a fertilizer benefit from the corn gluten.

September or October is actually a better time for the 3rd application but one in August is OK - just don't overdo it.