I have had very good success with upgrades clearing for the wife and I between IAH and PHL. The few times the upgrades did not clear was usually last minute bookings and IAH to MIA on the 4th of July weekend, the MIA to PHL did clear that same weekend. A number of the upgrades cleared at about the 72 hours mark. The odds of the upgrade clearing are better if you fly on Tuesdays and Wednesdays.