In reply to domainsley:
did similar to your plan (minus paraglide) in about a day an a half. you will only do it in 1 push if you are an experienced ultra runner, doing it in under two days is fine if acclimatised. i bivvied on the balcony/ledge of the old gouter hut, one of the best sleep spots of my life! fantastic sunset and really comfy spot. hid my bivy kit in the remains of the old hut for a lighweight summit day. i dont know what if any of the old hut still exists (it was only about 4 years ago) but i imagine you will find somewhere in the vicinity. i planned on waking up at 2am but got woken about 1am by a team who were on their way up from the tet rousse and stepping over me... other than them i had the mountain to myself untill i reached the summit and sat waiting for the sun to rise for about an hour! it was the usual circus on the way down.
in short, sept is a great time to do it, less punters and things are freezing up again. as for when, all depends on the weather forecast