Once I was over in Japan witnessing factory acceptance testing on behalf of a client; the testing was for equipment that would provide an inter-site connection across a world-wide set of ground stations (never actually deployed, but that's another story). The testing was scheduled to be conducted over about 1.5 days, with another half day as contingency (I had insisted on that - in my experience, Murphy's Law *loves* acceptance tests).
Everything went well until about halfway through the afternoon when one of the critical test had failed, badly. Repeated attempts resulted in the same wrong behaviour. As it stood I would have to fail the entire test campaign which would have left the project team with a major loss of face (this is Japan, so loss of face is treated very seriously). I discussed things with the test manager and suggested that I just settle myself into a chair in the corner of the room out of the way while his team tried to sort the problem out. This offer was gratefully received since it would allow them to at least avoid the official black mark that was heading their way.
By the end of the day the problem had not been resolved and I headed back to the hotel. The next day I came back to site and was greeted with a beaming and still very grateful) test manager; they had found and fixed the problem at about 2:00 am in the morning (it turned out that they had fumbled reconfiguring routers from one mode for testing to another mode, resulting in the router having some form of weird hybrid configuration that could not do anything sensibly). The downside is that the factory doors had been locked at 19:00 so the staff fixing the problem had been locked in and had to sleep on the floor.
Testing was successfully finished that day using some of the contingency time I had insisted on.