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!

I strongly second all of the above.

Thanks for the advice; I'll wait until June or July then.

My next problem is how the heck will I overwinter them? If I do get some roots by the end of July, I'm guessing the cuttings will be nowhere near strong enough to go outside into the ground when I live in zone 3! Could I cover the cuttings in a bag, and put them in the fridge?(to mimic the dormant stage)

I'd store the rooted cuttings for winter someplace where they will remain dormant yet not allowed to freeze solid....an unheated basement perhaps or garage that stays right around freezing? Light really isn't a concern, it's the temps that are most critical. If you can shoot for 40-35F you should be good. And then you will gradually need to wean them into light and higher temperatures when winter is over and it is safe to leave them outside.