Ah Ha! Thank you, room temp in my kitchen is 76 - 78 or so if I cook inside, which isn't bad for the desert (not using the evap cooler), But that explains why, 2 days later, it thickened again overnight using the buttermilk as usual. It only gets hotter here till October so, I could set it outside, covered and varmit proofed. It gets quite cool (65ish) at night.
Alternatively, do you think I could start in the morinig and just let it sit a five or six hours? I could throw some litmus paper at it to determine acidic pH.