I chuckled, yes I agree it would be "on" that day? What would make her blow off work to spend the day with him? She would have to understand she would likely lose her job, right? They were trying to reach her and she did not take the calls?
I am curious about the nature of their relationship as well. It also makes sense why she would not tell family, friends or the babysitter she was visiting the ex, if everyone considered it a "bad" relationship.
Work stated she left for lunch at 1, the babysitter said she spoke to her at 3 or 4 and they spoke about her new job at the car dealer. Did she give the babysitter the impression she was at work at that time? Do we know if she was caught on CCTV arriving at the apartment? Was she there since right around lunch or was she just arriving at 5:50?