How long has the worst tornado stayed on ground?

The worst tornado in U.S. history, the Tri-State tornado of 1925, was on the ground for 3 hours and 29 minutes. The worst in world history, the Daulatput-Saturia tornado of 1989, had a path length of 50 miles but it is not known how long it was on the ground. However, given the path length it was probably on the ground for an hour to two hours.