Here is a recent post in another thread. Seems like 8-10 weeks has been most common for the pre-approval to come through.
I just spoke with my lawyer today and she received a preliminary approval for another client yesterday and that one took 8 weeks from submission. She said in June/July they were running about 10 weeks which was in improvement from as high as ~18 weeks last year. The “normal” processing time is ~6 weeks so it seems like things are getting better (…at least until the flood of applications rolls in at the end of the year).