Contador is 2 minutes behind Evans. Ideally Contador will want some margin over Evans for Saturday's time trial as both are pretty much equal in that event.
Now, he's not going to make up 2 minutes or more on Evans on the Alpe d'Huez, so Contador really needs to strike tomorrow or it will be too late.
The Galibier ascent at the end will be very harsh; 23k going over 2,600m altitude and with all the steep parts in final 8km. And of course they also have to climb over 2 other similar colossus mountains immediately before they reach the Galibier. The stage looks impossible on paper.
I think there'll be massive time differences tomorrow between some of the favorites. The Tour will be decided tomorrow!