Bob,

It may be the strains that you have chosen to grow since different strains will mature at different rates and we all know that the last couple of weeks of flowering show the greatest bud development.

For example, I can finish a bacth of good Northern Lights in about 6 weeks where Thai, Haze (or some other Sativa) might take as long as 10 weeks to finish.

Sativas do not seem great "cash croppers" unless you're growing 12 ft tall plants outside on a pot farm.