As we don't know exactly what happened I don't think we can say for sure that it was heat of the moment.
The nature of murdering three people, and we don't know what kind of time was between each murder, would imply to me either psychosis or that at least the second two were premeditated.
My understanding is that legal premeditation is not exactly how lay people might think it is, and it might be that the legal thing is that once you've got your hands around someone's neck, when you decide to not remove your hands, then you've chosen (premeditated) to attempt murder. I'm not a lawyer so we need legal clarification on that point, as we might be wrong if we assume that a heat-of-the moment reaction that ends in murder is automatically not premeditated.
CW's post-murder reaction does not suggest psychosis was behind the murders.
I am reading people using the word 'motive' for these murders. It's possible there was a motive in the usual sense of the word. I wonder if it was more that a trigger point was reached, which I think is different from having motive, but in no way automatically means that there was no premediation. In a lot of ways it does seem like there's probably associated motivation (I'm tired of putting on this doting daddy act, I want to be free and go have girlfriends and not be tied down by a wife and children (and one more on the way!).
Anyway, my point is that even a premeditation period of one minute would mean that he didn't have a pre-existing plan for clearing up and scene-setting and disposal. I think his plan was limited, but might have been that he'd do whatever clearing up and disposal before work, and then come home after work and anything he thought of in the meantime ... making sure to say he came home to an open back door and maybe throwing out the bedding and Shanann's purse, could be finished after work. But Shanann's friend turned up at the door and blew his chance to finish off the clearing up and the scene-setting.
So, to sum up, not completing all those things before going off to dispose of the bodies in no way automatically means lack of premeditation.