My personal experience is that the notion "I will go in early today and leave at an appropriately early time," fails to work out as planned 90-95% of the time.

But I really can only blame myself for this.

Pre corona I was arriving at 7~ and leaving at 15. You can definitely do it.

Same. This was my schedule too, and maybe I got lucky in my workplace, but after socializing about it, nobody had any problem with the leaving earlier part.

Was easy too, 'can we meet at 4:30' 'Hmm, I come in pretty early, and like to get out the door by 3:30, can we do it earlier?' was a typical exchange.

Also, depending on your office arrangement your team-mates just know you get in early when they always see you in the office when they get in. But, ymmv, I am sure it varies from workplace to workplace.

It almost seems easier to pull off if you leave exceptionally early (3pm or earlier). E.g., if you leave at 4:15pm, that doesn't give any reminder that you started early.

You have the discipline to use the 24 hour nomenclature all the time. I applaud you! I had to read this twice, and loved it so much I had to comment

I find early better for few reasons, but primarily because not all work hours are the same. Waking up, working out, then immediately doing deep work before checking my phone, internet, or anything else almost feels like a super power. The best work hours of my day are actually spent working, and are almost never interrupted. Even if I do have to attend a late meeting or something, my brain is in the wind down mode and shouldn't need to wind back up. This means it's easier to fall asleep, and repeat the next day.

I used to do the stay up late thing, and while work did get done, it's nowhere close to what I get done in the morning.