How long do shipments usually stay in "Processing"?

MAPinnick thought this was worth mentioning said

I was lucky (and fast) enough to get an IRK on June 24th, and according to the tracker it soon went to the “Processing” stage…where it has been ever since. Now, I have read of incidents where people have received their shipments while the packages were supposedly still in “Processing”, and I was wondering if this was normal or not.