You do not specify where exactly you are or what kind of hydrangeas you refer to so this is like shooting in the dark, but I'll bite.
Yes.

Whoops...left out some main ingredients.
I live in south al and they are macrophyllias. Endless summer.

Should work. 90 minutes of direct sun shouldn't be enough to fry them. Just make sure the morning shade isn't too deep, which would retard bloomage.

Thank you all