@meishere30 I'm a hippie not a knee-er here but just happened to see this thread.
It sounds like your dad has an advantage plan. They are indeed the primary and have a fit if anything is billed to medicare instead of them. The elective thing only means that this surgery isn't a a medically urgent or life or death type operation, like an obstructed bowel or broken hip.
My surgeon assumed I wanted an overnight in the hospital, but I asked for a same day release. He was OK with that because, according to him, if he schedules for same day he is able to order another night(s) if the patient isn't ready to go home. That includes medical reason like low BP, or functional reasons like not being ambulatory or being a fall risk.
But if he schedules for overnights, he can't release his patients early.
When my sister had her surgery, she had a problem on the day she was supposed to be released (a day or two in the hospital). She wasn't able to do stairs or bear any weight on the operated leg. So she went to a rehab facility for a few days, where she got the nursing care she needed and the appropriate PT to get her moving.
Talk to the person at the surgeon's office about all this. They will most likely explain everything to you, or be able to run interference with your dad's insurance.
Good luck to you and your dad.