Strawberry runner when to cut

[ChelswannabeGT]

when do I cut it after it makes new plant?

 

[headfullofbees]

Let it open a couple of leaves and wait a week.
I usually wait until runners already have leaves, and find that from there, it's ten days max.
You're starting both together, which overall may take slightly longer, but should be just as successful.
Tomayto/tomahto.