I feel the time should be dependent on batch size as well as number of cores, speed of each core,  io speed,  ram, cache limit etc etc. Don’t you think so?
The number of cores limit the number of threads that can be run simultaneously. The number of images in batch tells us that the dataloader can return the data only when all the images in the batch are loaded.
I haven’t had a close look on a minute level to compare the effect of batch size Vs. Number of workers. But from a naive straight forward view,  to me,  the performance depends on both. Maybe, let’s see if any other experts/experienced user’s have a different view on this.