The classic Pomodoro — twenty-five minutes on, five off — was written for office work with lots of small tasks. Gaokao prep is the opposite: long, hard sessions where you are trying to hold a whole problem in your head.
Move the base unit to fifty minutes on, ten off, and keep the phone in another room during the fifty. The break is not for scrolling. Stand up, drink water, look at something twenty meters away.
After three cycles, take a longer break — thirty minutes, ideally outside. This is the part everyone skips and it is the part that keeps you honest for six hours instead of two.
One useful modification for math and physics: if you are mid-problem when the timer goes off, finish the problem. The rule exists to serve the work, not the other way around.