Typically I start taking measurements on the pumpkins starting around day number 10. And then periodically, if not daily, take measurements after that. Sometimes you can recognize problems early if you find that growth is slowed down. A day 10 measurement doesn't mean much. Typically I want to see a pumpkin around 20-24 inches on day 10 for a Colorado grown pumpkin. However, I know growers in other states who consistently have day 10 measurements in the 15-19 inches range who have consistent 1,500 to 1,800 pound pumpkins at the end of the year. Weather and genetics can be a factor for how your pumpkin grows and ten days is a pretty small window.
The measurement on the 1791 pumpkin was a bit of a disappointment. 17 1/2 inches. The 1421 Stelts had a day 10 measurement of 23 1/2 inches last year. One thing I re-learned last year however is that it doesn't matter how they start, it only matters how the finish. The Wiz at mid-season last year had a very ordinary looking pumpkin. At the weigh-off it was the 2nd heaviest pumpkin ever grown in Colorado. His pumpkin was what is called a long grower. It never got to super high daily gains. It just kept growing consistently and never tapered off much. Although not as exciting, that is really the pumpkin you want. Less risks of the pumpkin splitting open when it is a long grower (although Wiz's pumpkin did unfortunately pop at the end of the year on a deep rib).