Don't pay too much attention to the one-size-fits-all label rate. The extension's rate sounds reasonable to me.
The 18% free sulfur is the only sulfur in the product that you posted that will work towards acidifying the soil. The rest is in the form of gypsum, which won't effect the pH.
Calculating it with 18% sulfur rather than 30 to gets you 0.55 lbs. of the product per 100 sq. ft.

Thanks, I will stick with the recommendations of the county extension then.

I am using agricultural sulfur to lower pH around our blueberry shrubs, for 14 years now, so I know how to apply and also how to measure pH. Sulfur is not an acid, it must be metabolized by bacteria in the soil, and slowly converts to sulfuric acid, over time, typically one year. The soil pH will be variable during this time, and after all the sulfur has been used up, it will very gradually rise, due to the effect of the surrounding soil and subsoil. If you are watering your roses with tap water that contains calcium and/or magnesium, then the pH will rise over time. Soil pH can be measured by taking a soil sample, mixing it with distilled water, and filtering the mixture to get about one teaspoon of filtrate. This sample is then mixed with several drops of bromothymol blue indicator, and the resulting color indicates the pH. Blue = pH 7.6, or higher. Yellow = pH 6.0, or lower, and varying shades of green mean the pH is between 6.0 and 7.6.

Theoretically the percent of sulfur is that much in each boc or bag you buy. In this case, if what you purchased is a one pound box, 30 percent of that would be sulfur or roughly one third of the box. Then to meet that 1 pound per 1,000 ft2 need you would need to purchase about 3 1 pound boxes.

ericwi,how much sulfer do you put around each blueberry bush? Do you apply each year?

This reply is for mntenz7tn, above. Each blueberry shrub gets 6 ounces, by volume, of agricultural sulfur in the bottom of the hole, at time of planting. After the shrub is in the ground, I put another 6 ounces, by volume, of agricultural sulfur, covering the ground to a radius of 16 inches. Next I apply about 6 inches of shredded tree leaves as mulch, so the sulfur is covered up. The initial application is good for two or three years, and after that, I might apply 1/4 cup of sulfur, every other year, but only if a soil pH test indicates a need. Our native soil is quite alkaline, pH = 7.6, and our tap water also has pH = 7.6. I test the soil around our blueberry shrubs twice a year, in the early spring, and again in the fall.

ph at 7.8--1750 sq foot how much sulfur

What's your pH goal Victoria?