Is it even possible for the cement to set in 20 hours, the time frame givien in the article?
Back when I was a roving cellular telecom engineer I supervised the construction of over 5000 cell towers all over the USA and in other parts of the world. It was typical to allow the tower caisson(s) to cure for at least 21 days before test plugs taken from the same concrete pour were compressed to the point of failure to check the strength of the concrete before we would stack the tower. They may be using a different type of concrete here, though.
Anytime I've worked with cement, the stuff usually sets about 5 minutes after I finally get it mixed!
Setup time depends upon a number of factors, one is the amount of calcium chloride is used in the cement, or how “hot” it is. I’m not sure of the particulars in this instance, but there are too many fishy things about this whole accident. There are safeguards in place to prevent this from happening, proven blowout protectors,I’m beginning to think the rig was blown up by someone.