[autoroll] Chromium->Skia roller only rolls between midnight and 4am EST
[autoroll] Chromium->Skia roller only rolls between midnight and 4am EST

We're already trying to do this will the roll interval; now we can use
an explicit time window instead.

Bug: skia:8627
Change-Id: I588d3c217a6f36ee3cbd08c97cb82ffcd1bb855e
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/204220
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot