Rule of thumb for taking breaks when hiking

Greetings fellow hiker!

I have been a pretty avid hiker for 20+ years.  Recently, I heard a fellow hiker state that "rest breaks when hiking should be less than 5 minutes or more than 20 minutes to avoid a lactic acid build up".  While I love this rule for time managment when hiking with a group, I cannot find evidence to support the justification of less than 5 minutes or more than 20.  If anyone could provide supporting evidence or give other evidence for this rule of thumb, it would be greatly appreciated.  I often lead groups in hiking and I certainly don't want to be using false information to manage the outing, the proper education can really enrich the experince.

Thank you,