If your Rolex watch stops at night, there are several possible reasons why this may be happening:

1. Not enough winding: If you have a mechanical Rolex watch, it may stop running if it has not been wound enough. Mechanical watches require regular winding to keep the movement running smoothly and accurately, and if the watch has not been wound enough during the day, it may stop running at night.
2. Power reserve depletion: Mechanical Rolex watches have a power reserve, which is how long the watch can run without a wound. If the power reserve has been depleted, the watch may stop running until it is rewound.
3. Magnetization: Magnetic fields can interfere with the movement of a mechanical watch and can cause it to lose accuracy or stop altogether. If your Rolex watch has been exposed to a strong magnetic field, such as from electronic devices or magnetic closures, it may stop running or lose accuracy.
4. Water damage: If your Rolex watch has been exposed to water or moisture, it may stop running or lose accuracy. Water damage can cause the movement of the watch to malfunction or rust, preventing it from running correctly.

If your Rolex watch is stopping at night or experiencing other issues, it is important to have it checked and serviced by an authorized Rolex dealer or watchmaker. Regular maintenance and servicing can help prevent problems and ensure that your Rolex watch runs accurately and reliably.