I'm hesitant to say much more about this crater, given my confusion with filters (see below, it was JPL's fault!), but I don't think it's a thermal emission issue.

The near-IR filters are looking at wavelengths just longer than visible light,and something has to be really hot to glow! For something to radiate much at 750nm it needs to be just about red hot, and even at 1000nm it's still more like a soldering iron than a sun-warmed rock.

The thermal IR bands on Odessey (THEMIS), for example, are 6,000 to 15,000nm.

But, time of day does sound like a good explanation for the difference, but due to the crater rim being shadowed in the morning shot.

At 9am, that crater would be due sunward -- the sun would shining from right over the crater, about 45 degrees up. So, the east side of the rim (the far side) would probably be shadowed.

At 3:30pm, it's the opposite -- the eastern rim catches the low sun in the west full on and is brightly illuminated.

So, my bet is sun angle, and that what we're seeing is that its very bright in reflected near-IR sunlight.