Meanwhile, I've got a related question about pre-flashing HDPP, for how long does the pre-flash last?

I tested and found the time to pre-flash, 150C/150M/150Y on my LPL6700, 75mm f/16, 18" up (enough to cover my 11x14"), came to 7 seconds.
I specifically closed the aperture and dimmed the light on purpose to lengthen the time, being 1/2 a second out on 7 seconds isn't much compared to being 1/2 a second out on a 1 second.

So I flashed a scrap, took it straight outside in my pinhole suitcase, gave it ei6 including the yellow filter gave 1 min in full sun, came out pretty well (maybe a 1/2 a stop too dark).
Then I flashed a full 11x14", loaded it in the suitcase, and left it overnight. The next day, pretty much 24 hours after I flashed it, I exposed it, same ei6 gave same 1 min, but gave it an extra half a stop to 1:30. took an hour or two to get home and get myself together to develop it.

Now, the results aren't bad, but it does look a lot more contrasty than the test strip. It's hard to show in a scan (not least because the paper ain't exactly flat, plus they're different subjects, but at least both were full sun), but I certainly see more separation of tones in the test (house) than in the big shot (beach). Neither are particularly blown out, but there's a lot more shadow detail in the bricks and flowers than in the sand/sky.

So did the pre-flash wear off? Is there any way to compensate besides flashing for longer depending on how long it'll be before shooting?
Of course shooting sooner is preferable, but I wanted to test this on purpose because I'll be away from my enlarger for WPPD on sunday and want to flash before I go, maybe on Fri or Sat
ps, I read someone somewhere say something about 'excited electrons', but surely a pre-flash is just taking an image of a light source, so should be affected by the same rules as latent image stability shouldn't it? (and if an image of a light source wears off after 24 hours, would a regular image do the same?)