- A decision is expected within four to six days.
No. A range provides a beginning and an end; ranges make no sense with within, because within comes equipped with its own beginning: now.
- A deal could be announced within the next week.
No. In! In the next week makes perfect sense.
- If the letter does not arrive within five business days, the deal is off.
Yes! That's what the word is for. The meaning isn't in five business days, because that would exclude one, two, three and four business days.