The buffet opened at 4PM, so my wife and I arrived 30 minutes early and signed up for the card.
I thanked her and had a nice experience with her. After several minutes on hold, she verified that the discount would be applied upon receipt of a Player's Card. I was unable to verify on-line whether or not this was true, so I called them and spoke with a representative who didn't know anything about it, but was kind enough to check.
My wife and I were told that the Hard Rock offered a 50% 'Senior Discount' on Wednesday's for their buffet, to those 55+.