Well, you can let them run a few weeks longer. The Black Creams I grew I would chop at 11 weeks, with seeds I let them go to 13/14 weeks. More amber, but the plant was still living and doing its thing. I mean LOTS more amber going 3 more weeks, but since the goal was seeds. I let em go.
Only thing is you wanna give 5-6 weeks for seed development. And remember, many seed vendors provide optimistic numbers, so when they say 8 weeks, it might be 8-10, and that plant can possibly live even longer, just going more and more amber. So its what your goal is at that point, seeds, or bud to smoke at the amber you prefer.
You can also pollenate now, and again in a week. Chances are you will get more seeds than you were planning for as long as the pollen is still good. Its pretty crazy how airborne it gets and how many seeds it will make even in a controlled pollenation…