You can clone at 3 weeks it may take a little longer and your success rate may not be as high but its better then letting a good female get away. You don't need to pinch the flowers off if there are any. Make sure you use anti-wilt to keep them from drying out. One thing about cloning with flowers is if you use a humidity dome you run a big risk or mold or rot on the flowers from too much moisture. Anti-wilt spray eliminates the need for the humidity dome and will save you temperature and humidity problems. Donā??t forget about using a good rooting gel or powder. Only use Ph adjusted RO water and keep the root zone warm (not the water. Water should be room temperature. Warm water may cook the roots) How are going to root your clones?

Good luck