I take cuttings when the shoots are 2 inches tall. They take about 12 days to root well and can be planted in the ground after about 21 days. Tubers vary tremendously in how long they take to put out two inch long sprouts. Some do so while in storage and others take a couple of weeks of sitting in warm pots under lights. If you plant a rooted cutting in the ground at the same time as you plant a tuber in the ground, the rooted cutting will bloom 2 to 3 weeks earlier than the tuber. So, long story short, you probably have some time to take some cuttings and you will definitely have lots of flowers from the cuttings. I grow over 1000 dahlia plants from cuttings each year.