I would say now, before it starts into active growth in the spring.
But make sure the soil isn't icy or snowy. Try to do it on a dry but frost free day.

You could also leave it where it is and be a little ruthless when pruning, this always works well, when rejuvenating Viburnhams i prefer to do them between April and May, last year i cut down three large Viburnhams, Opulus, Bodnantense and tinus, these are now completly foliaged up and looking great, just a few of the leaves have been burnt by the severe cold.

You never realise how hunky some of these shrubs can get. We had one (Tinus) we cut right back but it never really got over it! We cut Carleseii right back too and something suckery tried to take over....so that went in favour of a buddllea or whatever! We have not had much luck with them. Just one tall one left on the back boundary that helps with privacy. It has white pompom flowers with a lovely perfume. Have no experience of resiting these shrubs but good luck.