Camel…will Galibier be open in the third week of May, or is going to be like Hampsten riding up the Gavia in a snowstorm ?
Agreed, the only way to do this climb is from the St Michel side. In fact, we better plan an 8 hour day and do the Marmotte route: Bourg d’Oisin to Croix de Fer, down to St. Jean de Maurienne, over to St. Michel, up Telegraphe down to Valloire over Galibier, down Lauteret, back to Bourg D’Oisin and up Alpe D’Huez. I am getting totally pumped up just typing this sentence. Now I have to figure out how to make this work on the home front 
Galibier 3rd week of May ?? Good question. I rode it early Summer 2 years ago, but not sure when, possibly mid-June. There was lots of snow on the ground beside the road, but not walls of snow and no problem on the road.
Last year I rode in the Pyrénées the 3rd week of May. Hautacam was no problem, with a bit of snow on the side of the road above 1,500m. Tourmalet was a no-go though, the road was blocked by snow above 1,700m. This would suggest the Galibier could be difficult. I rode the Gavia and Stelvio end of May last year, both around 2,700m like the Galibier. Both were cleared, although with huge snow walls on the side of the road. Stelvio was only cleared from one side, to access the ski station. An alternative pass in the region was totally under snow. That area is generally warmer than the French Alpes as well.
Last year I rode the Gran Fondo Campagnolo cyclosportif in Italy, it was mid-June and it snowed on the highest Col at 2,500m. That descent was painful beyond description !
On top of the Gavia Pass there’s a restaurant with heaps of Giro photos. They have big photos of snow on the pass during the Giro, I can’t remember but it was probably Andy Hampstead like you mention. No snow for me fortunately, but the snow walls were 20 foot high ! It was sunny and hot in the valley at 1,200m (around 90+ degrees). On the pass the weather and clouds rolled in and it was around mid-40s, crazy!)
The more I think about it the more I’m not sure for 3rd week of May. I was down there start of July hiking this year and it was no problem, but a lot can change in a month or so. I don’t know if there’s an official date when they open the pass or if it depends on the snow ? I think mid-June would probably be the earliest you want to plan for, apart from anything else it’s pretty painful descending some of those Cols when it’s cold, you freeze. I think mid-May you’re rolling the dice pretty heavily.