A contributor in Lincoln, Neb., dug up this archival item from the Lincoln Journal Star of Friday, June 15, 1951:
York Grain Elevator Work Proceeds Well
YORK, Neb. (UP). York’s new grain elevator had reached a height of about 95 feet and is continuing to grow about 6 feet each 24 hours.
Heavy rains of the last few weeks have hindered work somewhat, but progress was considered “good.”
Our Grandfathers' Grain Elevators 
Interesting to see the rate of advancement. I have always wondered what the rate was for hand jacked slipforms. I assume Tillotson was using hand jacks. My experience is limited to hydraulic and electric jacking systems. I recall on a single silo, 56′-6″ diameter in Gowrie, IA in the early 1970’s we slipped 24 feet in 12 hours one day shift. It was a perfect day for temperature, no wind, low humidity, etc. That was unusual. We normally assumed 10 – 12 feet per 12 hour shift. Rainy jobs were the worst. You had to slow way down to prevent having to much open form that would catch the rain and create problems.
Thanks for the insights!