Originally Posted by
fruitinspace
If you wait 15-20 minutes after takeoff, the cabin altitude should have pretty much reached its limit (8000ft or so), which is all that counts for your ears.
This is the answer that I was thinking of as well. In the US, the seatbelt sign goes off either at 10,000 or 18,000 ft. (might vary by airline). By that point, the cabin should be at the pressure that it'll stay at until descent.