I think a licensed surveyor, by his license, take responsibility for the work. S/He may have confidence in one crew over another, and may have to micromanage one crew, or may give much greater responsibility to another. He or she has to defend his decisions if there is a controversy. He may have a great deal of confidence in a particular employee that they will come to him for those more professional decisions. How about a person to properly file his records so he can refind them?
I don't think your putting a number on it is final. If the profession dictated exactly how many hours or what percentage of time the professional had to oversee the work it probably wouldn't be a profession.
Can the professional surveyor rely on an employee to do adequate title research? Can the professional surveyor rely on a crew that has proven they can find monuments even better than he can? Can the professional surveyor rely on an expert draftsman to do his drafting, or a scrivner to write a description?
I think the professional surveyor has to review all of these things, and whether or not he can have an employee take off and do a complete and adequate particular job might rely on his confidence level and experience with that person. If he lets crap get by him, he may find hmiself in hot water one day in court or explaining himself to another surveyor.