https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.infra.cron%2Fwpt-importer%2F1336%2F%2B%2Frecipes%2Fsteps%2FImport_changes_from_WPT_to_Chromium%2F0%2Fstdout shows such a time out case:
'
Timed out waiting for try jobs.
2017-09-05 22:09:21,422 - Timed out waiting for CQ; aborting.
'

And actually the CQ try jobs got a OK result later after the above time point. The win_chromium_rel_ng bot is the last one, and yes usually Windows bots are slower than other platforms.
https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_ng/builds/526899 shows:
'
End	Tue Sep 5 22:26:36 2017
Elapsed	1 hrs, 4 mins, 51 secs
'

Currently the time out configuration is 'TIMEOUT_SECONDS = 180 * 60', if we can make it 20 minutes longer, the above case should be OK.
So, can we just extend it? Or there are some reasons to adhere to 3 hours?
From my experiences on dry running Chromium CLs, seems if win_chromium_rel_ng bot did some retries, it would be easy to take time longer than 3 hours, although I have no concrete statistics data about that.