After all this, we might want to clarify what you meant by "testing hours?" Did you mean the length and comprehensiveness of the test list/test battery? Or, the actual full/total time spent for a modal neuropsychological evaluation (admin, scoring, interpretation and report writing)?
As
@PSYDR mentioned, you pretty much only get time to
diagnose the condition under most insurance plans (it is largely assumed that the diagnosis itself guides the treatment/treatment plan/treatment recommendations). i.e., "medical necessity." ASD might be a slightly notable exception here, as many would agree that multiple other factors about functioning need to be known in order to tailor treatment to the individual, since this is such a heterogeneous disorder/presentation.
Personally, I think over-testing is much more of a problem/issue than under-testing in our profession. I have come across both long and short test batteries that are pretty ludicrous and lack an evidence base for contributing to diagnosis and/or treatment needs/planning. However, I maintain that the more tests one gives, the more likely they are to find something erroneous/abnormal that may not actually mean much, clinically.
I am convinced that 12 and 16 hour long evals (as opposed to 6 or 8) don't contribute to meaningful treatment planning as much as they might actually "muddy the waters" for the people who are actually treating these folks. Which is usually NOT the neuropsychologist who did the evaluation. It's largely psychiatrists and masters-level practitioners.
Its important to keep mind mind that certain factors or features that psychologists/neuropsychologists might hold dear (or are curious about) in their assessments/testing are actually academic musings and not typically translatable to changing or impacting the treatment of said patient in any significant way.