I obviously don't have strong evidence one way or another, but I remain firmly in the "premeditated and it happened on Saturday" camp, which I know is a bit lonely but so be it. I don't think there was a long time of premeditation, even as little as 24 hours, but I do not believe this was a rage killing. I think it happened Saturday afternoon, and happened quickly. It's very possible there was a triggering conversation or event on Friday night, that she was going to leave him and maybe it reached an inevitable boiling point when he realized the implications of it but there was time IMO between that event. It may even have been, as other posited, a long con that started with their move from Indiana.
I think his nervousness on Saturday morning was due to jumpiness and anxiety related to having made his mind up to do it, or anxiousness to just get it over with, which is why he couldn't concentrate and left abruptly. I believe the leaving to go "make the wife happy" was just a lie. I don't think he went to actually try to make her happy, I don't think he really cared at all about that. He ambushes her there at home in the afternoon, perhaps catching her by surprise. He stashes her body somewhere, knowing full well everyone is out of town and he is in the clear, then goes out for awhile perhaps to try to establish an alibi for Saturday afternoon, makes last-minute arrangements for hotel, the so-called job, etc. then returns in the evening where under the cover of darkness on Saturday night he disposes of her then returns home to "leave for the day". MG's role in this I cannot guess except maybe to add credibility to the job or because he didn't want any questions from her? Not sure. She heard his truck at 4am - maybe he impulsively stopped at her house to see if he could talk but realized it was ridiculously early (or late, depending on your POV) and thought better of it. I do wonder if his plan wasn't originally to say she walked away in the middle of the night but maybe he thought the bike ride was a much better story and then set the wheels in motion for the "job".
The reason I think premeditation is the financial movement and motive that exists - how quickly he moved on selling the house, the Incapacitation, selling the other properties...these aren't the actions of an impulsive rage killer who then regrets their action...not to say someone of that ilk wouldn't position themselves to benefit after the deed, but to me it does show he had a pretty clear plan he executed against. He might not have been the best alibi and story planner, but he was sure shrewd and fast about handling all things on the financial side!
Fervently still wishing for a resolution and justice for Suzanne in 2021!