What is the resolution of your DEM? And how large is your study area? If the cell size is very small, and/or the study area is very large, it can take a long time.
If this is not the problem, then maybe there’s something funky about the DEM itself, in which case it would be helpful if you would post your entire datastack so we can try to run SDR with your data. Please see this post for how to create a datastack. Thanks!
My DEM resolution is 8.9 (9x9) and it is the whole watershed (HUC6). I ran my NDR model and the fill pits was finished for like an hour, but when I ran my SDR model, it is not progressing.
My file is over the maximum allowable upload here as it is around 1.9 GB. How can I send it to you?