Set exact night display last activated time

For automatic changes occuring precisely at a specific time, being
a few milliseconds off could lead to the system interpreting that
as a manual change.

This is most apparent when a time update occurs after restarting
the device.

Bug: 132844043
Test: atest FrameworksServicesTest:ColorDisplayServiceTest
Change-Id: I8de63f174a7e2f37623e04647bc55172a33730b8