You both make great points and it's interesting to hear how different peoples' thoughts and theories are from what I had simply assumed.
Regarding the lunch: When I lived in southeast Michigan, the Ann Arbor/Ypsilanti area was a big day-trip draw for people from all over, especially at Christmastime. I've seen a number of photos of Julia's family decked out in U of M colors (even with face paint, if I recall), obviously either heading to or gathered to watch a game on TV (despite that Julia attended a rival school). I just assumed that they had an affinity for U of M (as many in Michigan do; basically most people are either Wolverines or Spartans whether they attended one of those schools or not). There aren't a lot of towns around Monroe, so I just assumed that the sisters took a day trip to the Ann Arbor/Ypsi area for shopping and general hanging out and stopped by to see Julia since they were going to be in the area anyway, not that they drove all that way to shop in the Saline Walmart and see their sister. Things are pretty spread out in Michigan and an hour of driving isn't really considered a big deal or a long way to most people, at least that was my impression when I lived there. But of course I don't know either way.
Regarding the TV: I am surprised at that detail and somehow missed it in the affidavit. I assumed that Julia was in studying and set the alarm and may even have already gone to bed when the perp entered the apartment (or alternatively, that she had set the alarm and had begun to draw a bath when the perp entered) and that the alarm went off in the morning and that the perp was still (or back) in the apartment and silenced it. Alternatively, I assumed that the perp actually didn't enter the apartment until after the roommate left in the morning and that the murder took place in the morning. I'm kind of surprised that she had an alarm clock because I thought most college students just use their phone for alarms.
Did Julia take baths often? It wouldn't be usual behavior for me to take a bath in the morning (and I'd only marginally more likely to take one in the evening... but if I did take one, it would likely be in the evening when I was not in a rush), but this is all reminding me that people have very different habits.