Does the timer start on first input in 1.16.1 RSG or does it start when I load in the world?

just press esc and unpause when you start

it starts on world load but if you pause the game before the first blocks or mobs appear on the screen, it starts when you unpause

Due to how hard it is to predict exactly when the timer starts, the rules let you start the timer up to 1 second after the world loads as long as you don't do anything (including looking around) during that second