After Import is done, CullAi automatically starts analyzing photos to detect faces, calculate AI score, detect similar photos, auto pick photos and detect important people. It also displays imported photos, and user is free to browse them till analyzing step is completed. Most of the other features are disabled while analyzing photos, as they need analyzed information to work.
As this step is computationally intensive, overall time taken is related to processing power of host machine. CullAi uses Core ML for most of analyzing part, so it will efficiently use available resources for analyzing photos. If you feel it is taking long to complete, you can try reducing Preferences -> General -> Image resolution for AI processing. Higher resolution will have better accuracy but can be slow on older machines. For more details please check Troubleshooting Guide.