Can boxwoods be trimmed anytime?

yes.

You can trim boxwood any time of year but it's best to avoid doing a big trim in the fall. Those you want to save until the spring so the new growth is able to mature before the cold weather sets in.

Small pruning at a time and make sure it is not done on a hot sunny day.

I like to do a little trimming at Christmas time to make wreaths. I go in and clip out bunches of boxwood from the bush so light and air can get into the bush. I have found that just shearing the bush creates a dense bush and the bush tends to not do as well. In the winter, the bushes have gone dormant so new growth will not be stimulated.

Yes but Spring s best.