Wild guess, best time to get support if anything goes wrong.
Mondays and Fridays are bad as people take time off there, especially in US where folks want long weekend. Mid-week, generally fully staffed. Why you also see Apple & Microsoft software updates come out on Wednesday, Tuesday.
Companies I have worked at, generally won't push internal updates later than EOB Thursday, as don't want unexpected issues pop up for end-of-week processes/reports and noone around to fix.
So, Apple Pay, not only are you dealing with Apple, but also have payment processors and banks in the equation that have to deal with any potential issues and need to be staffed for them.