Avoriaz is easy from Morzine, you might even try and sneak up the evening before to see if the office is open. The descent down from Avoriaz to Morzine is one of the better parts of the ride, don’t miss that.
I started from Torgon in 2008, I’d say 50/50 as to whether it is worth it. A lot of it was over grassy fields. There was one ridge ride section which was quite good and the descent into Torgon in the woods was excellent. We had to hold our bikes on the ancient lift with the pedal providing support, that was cr@p.
As an alternative I’d try and do a few trails in Morgins or Chatel for example. You could use the time for an extra food and drink stop. Don’t underestimate the chances of a mechanical or two delaying you. Starting from Morzine you are at the far end to Torgon.