Being in Arlington TX, all TREC requires is to have 2 faucets on at the same time and then flush the toilet. If the flow drastically changes, write it up.
Did you by any chance do your training with AHIT? If yes, then the measuring cup thingy was to fill up a 2 cup measuring cup in 7 seconds (pretty much what Jamin said). The reason behind this was to know how many gallons of water went down the drain in X amount of time. Should something happen, you would be able to tell plumber an estimation of how much water was used.
Over time, you won’t be needing the measuring cup as you will be able to look at the flow and guestimate it.
This estimation can help you especially when the house is its own septic system.