If you travel 5 mph, that would equal 440 feet per minute. At 10 feet wide you are covering 4400 sqft per minute. So 4.4K times .25 gallons, means you need to spray at a volume of 1.1 gallons per minute. Catch the flow for one minute to get 141 ounces per minute.
At one ounce per thousand you need 48 ounces Trimec per 12 gal tank. Better to use the 1.5 ounce rate and use 72 ounces per 12 gal tank. Add a bit of surfactant (around 7 ounces per 12 gallon) for best results.
Naturally, you have to cut the herbicide in half for each 6 gal tank on the Triumph.