When can I cut clones from my females?

You need to have at least two nodes below your cut to get a healthy clone from what ivI've . Seen and been told

I'm here to grow the best meds that the soil can offer......

 

 

Like "Hemp Hugger" said, you need to have at-least two healthy nodes below your cut. In-addition to that, the cutting should be about 4 inches long (although this is not mandatory, it is highly recommended). Another thing to keep in-mind is that clones cut from lower branches seemingly do better/root faster. In the end though, it depends on each individual plant. It would be much easier for posters to answer your question if they had a picture of you're plant. 
 
That being said... all of your plants are big enough... the smallest one 21cm (about 8 inches) should have more than enough branches for you to work with. Hopefully you topped your plants early. If you did, then you'll have a lot more to work with (for cloning) - and a larger yield ta-boot!