Depending on the strain , each one have a different harvest window.
The og kush is listed as a 8 weeks strain so wait for 9 weeks as 8 weeks is with the perfect confitions & setup
The amnesia is listed a 10 weeks so 11 weeks should be ok 12 perfect
The bubba kush is listed as a 9 weeks so 10 weeks is ok.
If you have a magnifier harvest depending on the trichomes ratio , if you have none then the method listed above is good