At 4 am Milo was playing in the crystal litterbox again, so I picked him up out of there and then moved the litterbox back next to Domino's in the office.
I left the bedroom door open, and Domino snuck in to eat Milo's food and drink his water. Milo kept his position lying on the bed, and snarled a bit, but made no move to actually do anything. Domino looked at him and answered with her low-frequency growl noise, and went back to eating/drinking.
When I got up for real this morning, Domino was curled up in the bottom of a cat perch which until this weekend had been piled high with all the boxes from a month of online purchases. At the former apartment she would go in there from time to time, for no apparent reason. In the new apartment it is against the far wall, next to the piano, and has a great view of the front foyer, the bedroom door and the livingroom, a perfect little fortress. Strange but true, the first day Milo was home he tried out that nook and liked it, but hasn't used it since.
Sometime while I was in the shower Milo actually used Domino's litterbox. I could tell by the major archeological excavation which had occurred inside it. His box is still pristine.
They are getting used to each other. Neither of them appears to be interested in an actual fight or dividing up territory. Domino has stopped her horrendous yowling at me, and now I get a standard-issue meow from her when she wants treats. Milo has noticed this treat thing, and I think he'll be wanting some too. Probably after I run out of the wet food which he now gets a tablespoon of at night.
By the end of the week they may even be civil to each other.