15 days from the day you get the phone activated I believe.
To the OP, I have heard 15 days also, BUT you might want to check with VZW even if it's over, because they have extended the return period to Jan 15 for anyone who bought a phone during the holiday season (I'd imagine this is to assist people giving phones as gifts) so it is possible that they have also extended the period that you can add the insurance.
15 days from the day you get the phone activated I believe.
You are correct. I just upgraded my insurance a week or so ago on Day 12 or 14 and the guy specifically said that I had just made it under the 15 day period.
Like the other guy said though, give 'em a call and see if they'll make an exception.
yes if you are past 15 and they won't let you, just return your device, and buy another and then you have 15 days again. I'd imagine CS would just let you put it on instead of the headache that would cause.