Do you know the time of the smartphone is accurate?
You're welcome!
It varies slightly depending on the manufacturer or model, and as time goes by on the same phone, some time difference occurs.

Try MaruWatch!
It is a standard clock, seconds clock.
You can see how many time difference there are and display the standard clock in milliseconds.

If you need to check the exact time, try it such as booking tickets for a concert.

Try a mini-watch, too. You can check the time by always putting it on the screen.