There is a point in the day when your ability to focus gets diminished.
You might not hit it every day, but, some days you will.
See if you can notice it.
When I hit mine, it’s usually a physical sensation, that is observable. I’ll try to describe it: I’m working, moving along, after having been up all day, doing my usual things, and then, a little ‘voice’ (not with actual words – just a sensation in my body) alerts my brain to stop.
Once that happens, it might actually be time to … stop. Or, at least take a break. Perhaps even a 10-minute nap.
Look, it’s very possible to keep going, ‘power through it’, and continue working.
But don’t you want to produce your best work?
If your body starts talking to your brain, listen to it. Don’t ignore it.
Take a seat for a few minutes. Get away from your computer. Recharge.
Even better, if it’s already after ‘quitting time’, then, stop. You can accomplish more tomorrow that you can by pushing it over the limit today.