A gift is valid for 12 months. If you are on an active Rollover Plan you can use the Rollover Data or Minutes you've been gifted just like the other Rollover Allocation type on your account - there's no 7-day usage limit.
If you aren't on a Rollover Plan, you get access to your Rollover gift for 7 days. If you haven't used it all up before the 7 days, it will stay on your account for a total of 12 months, but you'll only be able to access it once you buy a Rollover Plan.