You have 30 days.
You'll get charged a restocking fee and will have to go through hassle with Apple to get it exchanged. I hate hassle but that's just me. 🙂
You don't have to do this all at once I don't think. Everyone else in your family can get their phones now and when you are ready to get yours all your family has to do is add a line to get one.
or if you are on their family plan now, and need to move over with them... then go buy a $14 go phone or something and use that as your phone in the meantime.
Where did you hear 30 days from?
It's 14, with a 10% restocking fee.
No restocking fee will be assessed on iPhones returned within the 14-day return period.