Depends on what time it's scheduled, and what time you come in. Could be anything.

If you're standup is first thing when you get into the office, your context switch is from a cup of coffee.

Absolutely. And if every member of your team arrives at the same time, and that time happens to coincide with "time to grab a cup of coffee then beat it to the room for the meeting" then sure, that makes sense. I haven't found that to be the case for most of the teams I've worked on.

I call BS. I can't for the life of me, find one consistent thing that can either get me into or get me out of a state of flow.

I can't identify one specific thing to get into flow state, but I can give you a laundry list of things that will break my "flow" once I get there. And having to go to a meeting is pretty much at the top of the list. shrug