Aux4ever -- "What is your average riffling time per tray of DPS?"
-- It can vary.
-- Some offices will use actual time, if "blockers" are not used, per page 34 of the Mail Count Guide.
-- In some offices, my old one included, the carriers at the office pre-count meeting came to an agreement with manglement to use 10 or 15 seconds [ forget which one -- last count was in 2011 ] per DPS tray. At that time, we had letter sorting machines in the office on one side of the work floor -- away from most routes.
-- This came about because the counter would have to go to the letter machine area to time the carrier riffling through the DPS trays. This took the counter away from the other routes [ 4 to 6, depending on the number of routes and number of counters ] for too long. Other carriers in the counter's group would just have to wait their turn to get timed for riffling.
"Are we supposed to go through it slowly and weed out all the missorts, forwards, etc…?"
-- To use one of manglement's old favorite sayings: "It is what it is!" when riffling through the DPS trays. The more letters [ 3M, holds, forwards, inverted, etc ] one has to remove, the longer it will take. For the most part, you'll really want to look for out of sequence letters for your route.
-- It just may come down to a "everyone or no one" vote by the carriers to use a "standard" time or actual time.