Final answer:
A nurse should scrub hands not visibly soiled for at least 20 seconds for effective hand hygiene, as recommended by the CDC.
Step-by-step explanation:
The minimal amount of time that a nurse should scrub hands that are not visibly soiled for effective hand hygiene is 20 seconds. This duration is also what is recommended by the Centers for Disease Control and Prevention (CDC) for the general public to perform effective handwashing. It is advised to lather the hands with soap, scrubbing all surfaces including thumbs, wrists, between fingers, and under the fingernails. To time this, one can hum the "Happy Birthday" song twice. Although for more specific procedures like surgical scrubbing, the protocol may be more extensive and the duration may vary depending on the antimicrobial used.