Ended up waiting for four hours, until 02:00, for the next Giant hot period. This was a pretty strong one, where Feather did not have to restart, and Giant did have some, but not a lot, of surging at the right time. Because of the cold, it was impossible to see much on the platform once things got started, especially back through the Mastiff runoff. But with several of the bright lights, we could see Feather and Giant itself.
Because the duration of the previous Fountain Geyser eruption had been reported as 36 minutes, we then went out to check on Fountain and Morning. That longer duration is one of the few signs that Morning might erupt soon.
It was a slow drive because we didn't want to have any close bison encounters. Got there to find that we'd missed Fountain by at least an hour, but at least we confirmed that Morning probably didn't do anything.
It appears Giant has settled into a mode it displayed last interval-- for several days we get a moderatly strong hot period every 6 to 7 hours. In between there may be a bathtub or weak Feather-only hot period. If this is the case, then any hope for a short interval (and for an eruption before we leave) is gone.
But the big news were the massive changes to the northern third of Geyser Hill, which started with a huge eruption of Ear Spring. I was hanging around waiting for the latest Giant hot period, so I didn't get over there until dark. But it was still obvious that things were different. I saw the murky mess in and around Ear. Both vents of Doublet were erupting to several feet. There was an Aurum eruption only a few hours after the previous. And under the boardwalk between Doublet and Pump there was the sound of either a frying pan or a drain hole (hard to tell in the windy conditions). Pump itself seemed weaker.
In any case, will have to visit again in the morning when can actually see things.