Used them for restaurants and got the confirmation emails right after the card was swiped.
Did the purchases post with Saturday's date as well? I wonder if this has to do with how restaurants authorize cards at one time and only settle the batch later on (maybe after midnight).
If you got confirmation why not call Amex and ask? And if you have, what did they say?
long story
I guess you'd have to fist start with why you chose to switch (from DP) to PC