I live in Zone 7b, along the Southern New Jersey Shoreline; and my calendar will be prepared with that zone in mind. When considering planting times, the crucial dates are that of the first frost and that of the last frost. Growing outside must fall between those dates. In Zone 7b, the last frost can be anywhere between April 1 and April 15.
My area is technically the North East; and my planting zone is higher than other areas around because of the tempering factor of the Atlantic Ocean. This is the north, however, and the growing season is not that long. For that reason, it is a good idea to plant seeds inside at least a month before time to transplant outside.