Wilkens Masonry, like all brick and masonry restoration companies, shuts down it's small exterior repairs division with the arrival of sub-zero temperatures. Mortar needs to have a certain warmth to properly cure (set) and it's just not feasible to work with frozen mortar.
When there is an emergency, however, there are certain additives that can make a small repair possible. It may affect the aesthetics of the repair, but if it's an emergency, that should be alright!
Also, getting on the list for a spring repair is a good idea as the hustle and bustle of spring home repairs means you may not get tendded to until the summer!