How long after an ultrasonic fat cavitation/rf session on my face, is it safe to breastfeed my baby?

Depends: Did you get any sedation ? If you did not and there were no IV medications 24 hours sound like a very safe number.

Not certain: I'm not certain but don't see why that procedure would cause any difficulty with breast feeding.

Should be: Safe right away if you did not take any medication and they did not use strong medication to numb you on your face.