It appears that the system time for StackExchange is based on a server in a different time zone from myself. Where is this visible?
Everything at StackExchange runs on a straight UTC clock. You can see the current UTC time in the drop down menu when you hover over your name at the top of the screen, bottom left corner:
UTC Time HH:MM
All time based actions (such as the concept of a "day" as imposed by the per-day rep cap) operate on this clock irrespective of your current time zone, turning the page at 2400 hours UTC.