"Within the next week or so" means by the end of next week or a few days after that. So say I say this phrase on Monday April 7th, 2014.... then I have until around about April 21st / 22nd (because the end of next week is April 20th). The phrase "within a week or so" means 7 days from now or a little longer than that. So if I said on April 7th, "I will return the book within a week or so." then I have until like April 14 / 15th to return it. :)

It means the speaker will decide anytime from the day after to seven days after they make the statement.