Just wanted to provide an update:
I booked the Hilton Honors Discount, NON AP RATE. The charges were billed directly from the Chicago Oak Brook property and posted 4/2.
The remaining $250 resort credit posted today, 4/5, for $222. In addition, I had previously received an AMEX OFFER for $45 off of $250 on any Hilton resort.
This separate $45 adjustment posted on 4/4.
Going forward, I would avoid making an ADVANCED PURCHASE for a domestic Hilton property. The $250 resort credit should still apply, but it won't post automatically and you may need to fight with Amex for a manual adjustment.
If it is an International property, AP should be fine as it will be billed directly from the property.