I have a ton of privet hedges surrounding my driveway. I've neglected them over the past few years, and I noticed that they have become "top heavy" - growth on top, bare on the bottom. Today, I cut them down by about 1/2 (they are about waist high now).

Is it the right time to do this? They look pretty pathetic right now... when can I expect new growth to come in on these left over branches?