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I have read about how long this type of appraisal can take, and I think that it sounds like a grueling process at http://www.ctcappraisals.com/.
The appraiser has to go through a lot more things. The underlying asset doesn't even matter as much in the grand scheme of things like it does with residential appraisals.
Everything starts with a thorough inspection that can take one or more hours to complete. The appraiser has to go through a lot of aspects of the property like the zoning records, public ownership, and the like. Then they use other data like comparable sales, rental costs, etc. Once that is all put together, they analyze everything and come up with a report on what they found, which may take days to weeks.
In my opinion, that is a lot of work. However, it is essential if you need to find out what a commercial property's market value is. I know that I would go through it if I needed that information.