I'm having difficulty knowing when to crop an...

This is based on preference alot of people harvest when most of the trichomes are milky/cloud accompanied with some amber trichomes. Another way you could do it is to take the breeders suggested flowering time and add 1-2 week to that time . Really the easiest way to tell though would be to check the trichomes , you can get portable microscopes for cheap on Amazon or your local grow store . You could even go as far as to get micro lense for your smart phone provided you use one . This will give you awesome pictures of your trichomes . At the end of the day though it's all preference with a few guide lines to help determine . Based on what I see though your plants are still healthy . Still green . She will show you when it's close to time her leaves will yellow for seemingly no reason . I hope this helps you understand a bit more about selecting a time to harvest as well as some of the tools you may need to better help determine that factor ! Happy growing !