Hydrangeas in my zone 8A suffer when the summer sun hits the leaves/blooms and scorches them. Plants in warmer zones will suffer more if left unprotected. Heronswood is located in PA where this may not be a problem and some hydrangeas may be more tolerant of the sun but when you get to Zones 9-10 in places like CA/NM/TX/FL, do not chance it. The current Spring sun is fine and does not cause problems. Thus, try planting it where it gets morning sun and then shade starting at 11am to 12pm. I also have several ones growing in full time shade where they get a lot of indirect light. Dense shade can be iffy as it could affect their bloomage.

Another approach... if still unsure... leave it in the plastic pot that it came in and locate a place where you would like to plant it. Dig a hole and then put the pot and plant in the hole. Cover with mulch. Then observe how the plant does in the hot summer days. If the leaves and blooms are damaged by the sun during the summer (June - August), promptly move it elsewhere and see how it does there.