Shippers are driven by profits. They will load the trailers faster when it pays them to load trailers faster. They will change their methods when it profits them. Big shippers like drop and hook. It lets them load trailers at their leisure. They have a load by time. That trailer could be docked for 8 hours or more. Shippers can load product as they make it. If something more important (costs them more) comes up, the lift truck operator can stop loading the truck and tend to that matter. They will move in the direction of profits.
The industry needs to move towards overall efficiency. As long as holding up drivers does not cost 
shippers, they will delay drivers. It is great to see companies paying their drivers detention automatically. It is just as important to collect from the shipper. The problem will only get solved when it becomes less profitable for shippers to delay drivers. I believe that billing should start at the time of arrival/appointment.
When I was a warehouseman, we staged loads. That is we picked the load before the truck arrived. We had a warehouseman pick the order and stage it in front of a dock door. It might take up to 2 hours to pick and stage a load. To load the truck directly might take 2 hours and 15 minutes. When the trucker arrived they were told to back into the dock door adjacent to where the load was staged. Loading the truck took less than 30 minutes.
Break down costs into units of labor. Let's call each 15 minutes a unit. For the sake of simplicity, let's equalize the per unit cost of trucker time and lift truck operator time. As long as the truckers' time has
no cost to the shipper they will pick and load the truck, at the same time. It saves them 15 minutes, or one unit of labor, Since the shipper is saving a unit cost- and it does not cost them anything, they will pick and load, rather than pick, stage, and load. While it inhibits overall efficiency, it is in their own self interest. We all tend to act in our own self interest.
Say that each hour is worth $40. Each unit is then worth $10. By picking and loading it costs the shipper 9 units, or $90. The overall cost to the economy is 18 units. But, since the trucker represents no cost to the shipper, they will pick and load. When the shipper gets charged after 2 hours, they break even on labor costs. They will be paying 1 unit for the driver and it will cost them 9 units of their labor costs. That is the same as the 2.5 hours to pick, stage, and load. It could go either way. The additional space needed to stage the load may encourage the shipper to pick and load without staging.
Now, say that the shipper get charged after one hour. The overall cost to the economy stays the same, but their costs shift. Their lift truck operators cost for pick and load stays at 9 units, but their detention costs now rise to 5 units. Their overall cost is 14 units – or $140 to load the truck. If they pick, stage, and ship -their lift truck operator costs rise to 10 units. Their detention costs are eliminated. Their total costs drop to $100. Total labor cost to the economy also drops. Overall efficiency increases. That should be the ultimate goal.