[gkbrk]

Caffeine can take and usually takes way longer than 10 hours to clear from your system.

If you have 400 mg of caffeine in your body (max daily caffeine recommended by FDA), after 15 hours you will still have ~64 mg left. After 15 hours you still have the equivalent of 1 ounce of espresso in you.

[bayindirh]

400mg of caffeine equals to ~1.0L - 1.2L of filter coffee. Drinking it in one go is not that easy or common to begin with.

When you drink in 300ml mugs with normal speed, you clear the caffeine 10 hours after your last mug. That was my point.

If we want to skew numbers, we can take pure caffeine in powdered form theoretically, but that would be very unpleasant to deal with, and is not the mode of caffeine consumption I have seen around, to be honest.