Yes, they expire within 7 days - here's what it says on the order page:
"SAVE over $100! For a limited time, purchase a 2-Day with 3rd Day Free Ticket* and receive a second one free! Includes unlimited park-to-park access to both Universal Studios® and Islands of Adventure theme parks, plus admission to CityWalk® venues.
*Ticket expires within seven (7) consecutive calendar days beginning on the first day of use (and is non-transferable)"
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I thought someone posted that this offer was supposed to expire on 9/20, but I see that the web page still comes up.