I will say once you have done it a couple of times and have the spec sheet in front you, it only takes about 30 minutes to check, then set if needed then verify again.
The important thing is to make sure on the first point of reference is that both the cyclinders 1 and 4 are at top dead center on the COMPRESSION STROKE. Some mechanics and owners forget to make sure it is on the COMPERSSION STROKE because to do this you have to disassemble the throttle control for the motor and remove the magnetic injector pump sensor and verify with a hash mark in relation to a set of marks on the flywheel. Some just use the marks on the fly wheel as guidance but that is a mistake and they are setting them wrong.
But yes to answer your question it is very neccesary, most diesel mechanics can perform this check and adjust in less than .5 hour but will charge the full hour.