Hello, Mars44. Transplanting when the shrubs are dormant is the best time. Some people do this once they go dormant in the Fall. Others do it in the middle of winter if their winters are mild. And others do it just before Spring starts and before the plants have leafed out. Try to move as much of the root system as possible and remember to keep the potting soil as evenly moist as possible.
Remember that Masja blooms on old wood. That means that it has already developed invisible flower buds near the end of the stems for Spring 2016. Any transplanting will be a shock to the system and this can make the plant abort flower buds. So transplant while it is dormant to minimize blooming issues in Spring 2016.