The answer to 'best time for lawn' is that the best time to work on your lawn is in the spring and fall. In the spring, the cool temperatures and increased rainfall help new grass seed germinate and establish a strong root system. In the fall, the mild weather and cooler temperatures are ideal for overseeding, aerating, and other lawn maintenance tasks that prepare your lawn for the winter months.
It's generally best to avoid working on your lawn during the hot, dry summer months when grass is under stress. Instead, focus on mowing, watering, and light fertilization to keep your lawn healthy until the fall when you can do more intensive lawn care.