you mean standby off or complete power off?
I assume you mean cut power from TV. That´s not always a good idea because depending on the TVs programming it runs screen refreshing automatically after going to standby and if you cut power, this won´t be done and therefore the screen could be damaged over time.
So if you wanna cut power nonetheless, you should wait for at least 1hour to do so. Or you read the manual or similar of the exact model and how the refreshing is done on this.