I am running some tests on building overviews to see if the process can be sped up, but get confusing results. Using the define overviews tool in ArcGIS 10.5, I defined and built overviews for about 1,000 tiles of 6" orthoimagery. I used the default parameters and it created over 300 overviews and took 4 hours to build. I reduced the number of levels to 3 and increased the Overview Sampling Factor to 10. I also increased the number of rows and columns. This resulted in only 25 overviews, but still took 4 hours to build. How does it take the same amount of time to create 25 overviews as it does 300? I have tried different combinations of parameters, and it always results in a 4 hour process. Is there any other methods for speeding up the process of building overviews? The only thing I have found that provided any efficiency is creating them on the local hard drive as opposed to an external hard drive.