Upvote:6
I don't read the map as implying 7/8 hours from Canazei. It's 7/8 hours (counterclockwise, red on the map) or 6.30/7.30 (clockwise, blue on the map) just for the tour proper, including 1 hour lunch break. Based on my experience on the Sella Ronda, I would say that it's possible to be quicker if you have someone to guide you and you do not take long breaks. Conversely, you can easily loose time if you take a wrong turn, if you are not a very confident skier, or if you get tired towards the end of the day.
Having been to the area several times (including a couple of times in Canazei), I would add around an hour to reach Arabba from the village. That's an hour each way and you have to make sure to be back to Arabba in time to get the lifts to the top of Passo Pordoi if you want to go back to Canazei on your skis. Personally I can do the Sella Ronda in half a day but I never attempted the Grande Guerra (sounds like a lot of bussing around).
If you are up for it, I would highly recommend going on separate days to Arabba, Val Gardena, and Alta Badia and to spend time there to enjoy slopes like Gran Risa (a bit far but doable), Saslong, all the slopes down from the Porta Vescovo, and the Marmolada (on a separate day to be able to do it at least twice) instead. You can also go there on separate trips but there is more than enough to fill a week and if I have to choose, I would much rather do that than rush through the different resorts to complete a tour.