The Spot-HT settles in about a day, and much much much quicker than the B9R-1-Red.
I sometimes tilt the half full Vat and prop it up on one side, so that the higher part of the PDMS can breath between prints.
I tend not to leave resin in the Vat, however, I also have used a method similar to CarterTG. I took an old credit card, and I put the rubber wiper onto it, and used that to scrape up pigment from the bottom, and to oxygenate the PDMS.
If I do leave the Vat full overnight, I lower the build table down as low as it will go, as I suspect that some light can leak in at the top, but is less likely lower down. ... Also make sure that the build table is in "closed" position, so that light cant get in from the hole underneath.