Harvest when the soil is dry. Studies have shown that terpene levels are the highest to right before lights on. Extended periods of darkness is a controversial topic but many growers do a 24-36 hour dark period. If you do an extended dark period make sure you have proper airflow to help prevent mold. Personally I didn't see any increase in quality from leaving the lights out.
I usually harvest after my soil is dry. Then I have left them for 48h in darkness. There is some disgussion if that darkness is useful or not. It's not gonna harm your plant but anyways...
Happy harvest looking good!