The first bus of the day leaves Grand St. Bernard at 10:40, reaching Orsières at 11:30. That limits your ability to do very much that day.

Sightseeing in Sion or Brig might well be an option. In Sion a vineyard tour would be another option, I have no information to share, but the Sion Tourist Office should be happy to help.

More ambitious, and still doable, would be to take a bus from Sion at 14:00 and arrive in Derborance at 15:00, spend an hour and a half there, and take the 16:30 bus which would get you back to Sion at 17:30. Both the bus ride up the valley and the lake at Derborance are well worth the journey.