4,007. Things That Require Re-Sanctification

Hilchos Bias HaMikdash 5:3

A kohein need not sanctify himself before each form of service that he performs. Rather, he sanctifies his hands and feet once in the morning and may then serve all that day and into the night. This is only the case so long as he doesn’t leave the Temple, sleep, void his bladder, or let his attention stray from his hands and feet. If any of those things happens, he must sanctify his hands and feet again.

Hilchos Bias HaMikdash 5:4

If a kohein leaves the Temple, returns and resumes performing the service without sanctifying his hands and feet again, the service is valid so long as his attention never strayed. The general rule in the Temple was that no one could enter the courtyard to perform the service without first immersing in a mikvah. This was so even if the person was already ritually clean.