It depends on what your indoor growing situation is. Do you have lights, heat mats, etc? Basil seedlings can easily stagnate if not happy with their conditions. Also, with basil you don't plant out by the last frost date, but by the time when night temps quit falling below 50, which is generally 2-3 weeks later than AFD.

Thank you for the info, my growing conditions are good so will make the starting date to include the 2-3 weeks after our last frost date. Thanks again.