Fall is a good time to remove overgrown trees and shrubs and if you are not transplanting. Simply removing a plant - it does not matter what time of year you dig it out as the plant will not be reused. It is hard for some gardeners to remove overgrown plants as they grow so fond of things they have watched grow, but many shrubs and trees have a limited life span and start to decline over time. If you intend to plant the ceanothus or California lilac in place of the old snowball viburnum, I would wait until early spring, such as the month of February or March. This is because in your zone the California lilac is not very winter hardy and it would benefit from an entire summer of growing new roots before trying to survive a winter in a new location. One warning on the California lilac - the ceanothus family is short lived and this shrub will start to decline after just five to ten years in the landscape. This California native also needs very well-drained sandy soil, and prefers to be kept on the dry side in the summer. Keep growing, Marianne Binetti