@Antoine CHABERT Based on my experience with the service some of the details regarding like algorithms, training cycles, iterations used in the backend of the service are not made public so there is no documentation on the internals of the service.
With respect to training time the guidance on allocation of time is based on quality of images and dataset. Based on training budget the settings are decided for training that is a best fit. There is no specific relationship between the number of training images and training hours.