Is there a reason to delay taking the laptop in?
Wouldn't it be smarter to take it in, get it appraised so that you know the amount they’re giving you, and, if satisfactory, trade it in AND buy the new one right then and there?
Why risk taking it in up to 2 weeks later? You could damage it in the meantime; it could have a failure; and you might not get the amount you expected, anyway?!