In reply to Simon Cahill:
We did it from a tent on the Col du Midi.
Summit at 8 a.m. , back at tent 12:30. Had a brew, took the tent down and trudged back up the Midi. That trudge was easily the hardest part of the day. It was very hot, the snow was soft, and we were tired and loaded with our kit.
The Midi was seething with tourists and there was a long queue for the lift. Fortunately, the lady handing out cable car times (they do this when it is busy) gave us a ticket for the next one down. We must have looked knacked.