If the dock holds your truck, write the time in and the time out on the bill.
Detention is not a story you tell next week. It is two times on the paperwork. Federal safety staff have been asking how long trucks sit at docks. You do not need a study to know a truck that sits is a truck that does not make the next load.
Put it in writing while the driver is still there
The rate confirmation should say when detention starts and what it pays. When the truck arrives, write the in time. When it leaves, write the out time. Get the warehouse to sign it, or note that they refused.
If those times are not on the bill, you are arguing from memory. Memory does not get a carrier paid.