Maybe windows+py36 was failing because "456" is too small of a value, and the
OS time libraries can't figure out UTC for something back in 1970. Switch to
a fixed timestamp from just a few minutes ago, to see if it likes 2018
better.
For some reason, the appveyor (windows) tests fail on py36 with an OSError
during an internal (twisted.python.log) call to datetime.fromtimestamp().
It's possible that my mock times are too old (I'm using made-up values like
"456"), but maybe it's just that real time.time() returns a float instead of
an integer.
