Preload/twilight = no difference. Heck, twilight have more volume than preload, most of the preloaders in my building get one hour because the volume is that low. Completing a large trailer in 25 minutes may not be difficult, but most people can't do it. My back was aching me like crazy when I was half way, and I pushed myself to do it. Keep in mind that I did this by myself, and the metro that I used cannot go all the way into the truck, probably like halfway or less. So I had to pick up packages and threw it onto the metro about 3-4 feet. If the Metro could reach all the way in the back, I would be done in 12-15 minutes.
First off, the volume deviation between Preload & Twilight varies from building to building. I work one of the country's largest Preloads but on a good day our Twilight gets one-fourth the volume we do. That said, no Preloader in your building is going to come to work for only one hour. Especially in NYC.
That said, there's a tremendous difference between unloading on the Preload, as well as a hub->hub sort, and on the local sort (Twilight). The trailers that arrive on Preload are packed -- it's not uncommon to find a 100 lb. package, a 70 lb. metal pipe, or a 40 lb. package concealed behind a larger package - all on the top of the load in effort to utilize all available space. You can use all the methods you're trained; unless you're careful, you're going to get hurt (not necessarily severely). Plus there's over 70 lbs. / irregulars throughout the trailer (which need to be pulled, thus slow you down), as well as open boxes, damaged boxes & destroyed packages - all of which are time consuming to deal with. Plus you need to deal with SPA people and sorters (or, in an automated facility, the even slower camera system). I don't care how good you are, about 25-30 minutes is the fastest you can unload a pup -- and that's without any bulk, and with many larger packages. Not to mention that there's a big difference in unloading a trailer from CACH, which may be entirely lightweight Amazon boxes, and one from Detroit, which is heavy manufacturing packages.
And try unloading a 53' trailer here. We have to walk the final 10' off, since we don't have rollers that attach to each other. Ever walk several hundred boxes of paper realms off? Takes 20 minutes by itself. At the very least.