Started at 7:30 on a factory, it was -6C then did residential from 8:30 - 2:30. It only went above freezing about midday. We rock salted key area's, the water started to freeze on only a handful of windows but then the hot water melted it away. Even the windows that started to freeze didn't refreeze once cleaned, because the glass had been warmed.
I've heard of the hot water freezing faster than cold water stories, but to be honest I think in most real world situations thats a load of rubbish, hot water will get the job done in temperatures down to -10C from my experience. No broken panes either, not at the speed I was working in order to keep warm.
Simon.