Dude you’re literally providing the answer to your question and disproving a flat earth and why time zones exist
The reason it can be dark in New York and still daylight in California during a live football game is because the Earth is a sphere. As the Earth rotates, different parts face the sun, giving us day and night at different times. The Earth rotates once every 24 hours. As it spins, only one half of the Earth faces the sun at any given moment, so that half experiences daytime, while the other half is in darkness (night - like how it’s currently 11:29 PM in Beijing and 12:29 AM in Tokyo). When you’re watching the game from the West Coast and it’s still daylight, you’ll notice that the sun is beginning to set if it’s a late game (7PM LA time) but by 10 PM when the game is done, it’s dark out.
There’s 24 hours in a day, it takes 3 hours for the sun to reach its angle in the sky on the west coast (now 10 PM on the west) that already happened 3 hours earlier on the East Coast. Since the Earth is round and rotating from west to east, the sun appears to rise in the east and set in the west. This is why we have time zones.
Now, on a flat Earth, the sun would have to hover and spotlight only certain areas at a time for time zones to make any sense. But that doesn’t line up to reality because:
1. We’d see the sun from everywhere on Earth at once, it wouldn’t ‘set’ below the horizon. Go and watch a sunset for this effect. Even better at a beach.
2. The sun would have to shrink or fade out—not dip bottom-first below the horizon like it clearly does. You see this very clearly watching the sunset.
3. There’d be no clean dividing line between night and day, like we can see clearly see from high-altitude flights.
But I get the idea this will mean nothing to you and you’ll believe what you want