Marijuana plant timing

A question from a fellow grower:

I have a question about the timing of plantings.

I have ordered White Widow, Pineapple, Silver and Gold Leaf. I will be growing in a sunny room with ventilated skylights. I live in New Jersey just south of New York City. I want to grow one of each type this year.

Considering flowering times 60 to 80 days for the above is it best to do 2 plantings of 2 plants each one after the other, or just 1 planting of 4 plants in order to catch optimal sunshine for certain months in spring / summer? What is the best time / months of the year for a natural light grow?