Christ died during daylight hours on Wednesday.

They had to get Him in the grave before sundown.

At sundown (6PM) the new Jewish day starts. They were rushing to get Him buried before sundown by custom.

12 dark hours followed by 12 hours of light is one day.

So He's in the ground by 6PM Wednesday and by 6PM Thursday He's been one day in the grave.

Thursday 6PM to Friday 6PM is two days in the grave.

Friday 6PM to Saturday 6PM is the third day in the grave.

After 6PM Saturday He rises, which is now Sunday.

For clarity when synchronizing with Q posts.