Sts cutting

How old does a plant need to be to use sts
I have a fem cutting just rooted and I’m off flower so I wondered if I can use sts on a new cutting ?
I can’t afford to wait longer to flower and they need spraying a week prior so I wonder if I can start on this cut and have results

As soon as the plant material is rooted and healthy you can start to spray, if you're working from clones. Once you have a cutting the material is basically as old as the mom plant.

With STS I always spray 2 times before flip 5 days apart. Then flip and continue til I see male parts.

Good luck.