I had my Dawn Redwood in full sun, the leaves will send the energy from the sun, down to just above the cut, callous, and hopefully bud out in 4-6 weeks. Without at least some direct sun it will take longer.
I've never bothered covering it from light., I think that's pseudo-science, not going to hurt though. I always use clear so I can see if roots form without taking off a cover, your canopy will block a good portion also. I use a plastic meat tray over the top on a lot of mine to cover the rain (might be hard to do on that tree), I always worry more about it getting too wet from the rain. Zip ties are your friend!
The only thing I question is, did you scrape the cambium layer off with a knife or alcohol? It looks a little shiny, if you don't scrap of that "coating" It may just heal over and not shoot out any roots. Also make sure the moss is all the way around; the bag is tight to make good contact.
All in in all it looks pretty good for the first time...ring looks good. I think the "rule" is 1 1/2 time the diameter of the trunk/branch, IMO it should work though.
You should put your zone on your account; some advice will change depending on your location.