Clematis cuttings are notoriously difficult to root. Layering is much easier IMO.

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.

The information you've found is vague because this is an issue that goes round and round without any clear cut answers. You will see a lot of debate on this subject......there are many that find most maple species very difficult to strike from cuttings. Either the cutting doesn't take at all (largest percentage), fails to root successfully (root development not sufficient to support plant growth) or rooted cuttings somehow lack the ability to overwinter. By far the preferred methods for propagation are seed grown tree, grafting or less successfully, air layering. Now is not the time to attempt cuttings - trees are dormant/not in active growth and unlikely to develop roots. Cuttings taken in July from new wood that has hardened off will be more successful - try to take cuttings at least 8-10" in length and that contain at least 3 nodes. Use a rooting hormone, provide some warmth, even humidity and indirect light. And hope for the best. If your original tree was grafted and the cuttings you are taking are from the base or below the graft, understand that you may be growing an entirely different species. If your tree has produced any seeds, I'd try germinating them as a back-up plan :-) Growing maples from seeds is downright easy compared to growing them from cuttings!

hardwood cuttings are easy too. When you notice the new buds begin to swell in early spring/late winter, cut a few branches and pot them in a shady area. Keep them watered, uncovered, and let they stay in the pots until fall. Those that root will leaf out and grow. I did lots of these this past spring. Redtwig dogwood, not the red flowering tree.