He will have a week of total rest. I agree this Giro-Tour period is way too little time for another form building cycle. They indeed are aiming to prolong his top form by this rest period + training + another rest just before the Tour. It's a hard task but keep in mind that he's been in a great form since start of March with no signs of slowing down. They want to prolong it even more till the end of the Tour and according to a recent interview relatively small number of racing days so far (31) is the foundation of it.
There is also another possibility: he hasn't peaked yet and will do it at the Tour (only if it's possible that the Giro was a part of form building process...I will believe it only when I see it)
I'm not blaming Pogacar and his team to to try out the double. In contrary. It's fantastic for the sport and the spectacle. I'm just stating that Pogacar won't be able to perform at top level for the entire Tour. Which is good for his opponents and even more so for us, the audience. Pogacar seems to have become even stronger this season. If he would only contest the Tour and Vingegaard would also be in top form, I think the battle would have been very even. With perhaps a slight preference for Pogacar.
Pogacar with the double and Vingegaard in top form, then Vingegaard always wins (same situation as last year). As it looks now, with Vingegaard at 98% (or not participating), Roglic perfectly prepared, Bernal perfectly prepared, Evenepoel at 99%, then Roglic wins ahead of Pogacar, Vingegaard, Evenepoel and Bernal (although numbers three, four and five also could change places).