I've planted 3 new hedges in the past month - 25m viburnum tinus (60cm spacing), 12m Japanese box (25-30cm spacing), 8m sweet viburnum (80cm spacing). They were all 150-200mm pots.
I clipped them when I first planted and can see new growth already on them. However, I can't seem to find in all my googling how frequently I should clip them. I've seen one thread here that someone suggested clipping them every few months but that's it. So unsure if that's right or I should be more aggressive than that during this time of year.