It isn't too many trucks at one time. They simply take that long.
I am thinking of the Amazon in Joliet, IL.
Get there on time and they send you to a staging area where you will wait for a couple hours, or more.
Once you get a dock you will wait another several hours for them to unload it.
6-8 hours in to out, always, from my experience there.
It is the same for everyone, and the reason why I will find any reason not to deliver there.
As should every other driver out here, until they can clean up their act.
If places like that can not schedule properly, and have the people to do the job correctly, they should be shunned and banned by the drivers.