So, I don't get to just "step out" when I am on the clock (not on break or lunch) without telling someone where I'm going. And I have a flexible schedule.
From my point of view, it's odd to "step out" less than an hour into a shift. 5 minutes, ten minutes, just doesn't happen unless you are on a scheduled break, then you can do as you wish during your break. My experience over my umpteen year work life. So that is why I would consider it odd if someone did. Not something that would be acceptable in any company I worked for. You need to run to the car? You tell someone you are running to your car. You need to pass something off to someone? You ask if it is ok and say when you are going to do it. That is so if anyone needs you for anything during a time when you are not on your break, they know where to find you. It's also a safety thing so if a fire breaks out, they know who might be inside.
All I am saying is that in my experience, people don't just walk out of their workplace randomly without telling someone they are doing so, so to me it's weird. Doesn't matter the time of day or night. Anyone else's mileage may vary.