It depends on your dataset. For example, a single class (face, pedestrian or car) object detection model with ten of thousands of positive samples should take at least 18 hours to complete on a modern Intel CPU with a target FPR (false positive rate) set to 0.00001. The lower the fpr is, the more training time is required.

https://sod.pixlab.io/samples.html for some code samples.

Orders of magnitudes slower....