Seven days, especially if they will not get further cooking. Further cooking being to 145 degrees Farenheit. Freezer the time is based on quality.

You should be able to keep them in the fridge for about a month, but keep in mind that fresh egg whites are more stable and will give you more volume if you plan to whip them up into a meringue. And don't forget to mark the date on the container - I've done that so many times - I'm just sure I'll remember how long they've been in there. I keep mine at the back of the frig where it's coldest. If you need to keep them longer, you can freeze egg whites in ice cube trays and unmold into a ziplok freezer bag. They'll keep in the freezer for about 6 months.