The longer the better...

[Jim "Chocolate Thunder" Dennis]

Seven books, seven Horcruxes, seven years at Hogwarts, seven Friday
the 13th movies...before the other three and the "Freddy v. Jason" one...

I vote seven days, just to prevent the "Hey, did you read the book?"
"Yeah, it was great!  I can't believe Harry opened up a Muggle Chinese
restaurant with Crabbe and Goyle after turning Voldemort into Secret
Sauce!"  "Sure was great!"

The true dissection of the book can wait a week while we ALL take the
time to absorb/read it a second (probably a third) time...

Friartuck97