Gogo is offering 25% off a 24 hour pass.
It does not mention an expiration date on the landing page.
Thanks to Sice for the tip.
UPDATE: It is good through Labor Day. Confirmed by DL
UPDATE 2: The offer does not apply to purchases in flight – buy before you fly!
Is the 24-Hour Pass valid on AA?
I chatted their support team, who confirmed that there is no expiration date on the code you purchase, just must complete purchase by labor day.