It depends on which one you are referring to as there were 10 tornadoes in Montana in 2010. The two most notable are:
The Billings EF2 of June 20, which lasted 12 minutes and
The Sheridan County EF3 of July 26 which lasted 37 minutes (this was Montana's only killer tornado for the year).
The 8 others lasted as follows:
The McCone County EF0 of May 27 which lasted 15 seconds
The Carbon County EF2 of June 16 which lasted 5 minutes
The McCone County EF1 of June 16 which lasted 8 minutes
The Valley County EF0 of June 21 which lasted less than a minute
The Otter area EF1 of June 21 which lasted 10 minutes
The Powder River County EF2 of June 21 which lasted 10 minutes
The Park County EF2 of July 2 which lasted 7 minutes
The Wheat land County EF0 of September 9 which lasted 5 minutes
As of May 16, 2012 the last tornado was two days ago.
Hannah Montana was on for four seasons on the Disney Channel. The last season production ended in 2010 and the last episode went on air in January 2011.
There is no given duration for a tornado of any intensity, but a tornado as violent as an EF5 will generally last fairly long. Most will likely last for at least 20 minutes. Some may last for well over an hour.
It varies. A tornado warning may last for just a few minutes or over an hour.
3.5 hours
The worst tornado damage of 2010 appears to have been in Mississippi, particularly from long-track EF4 tornado that move across the state on April 22.
The average tornado lasts about 15 minutes, but they can last anywhere from just a few seconds to several hours.
3.5 hours
4 mins
3.5 hours
The Joplin, Missouri tornado of May 22, 2011 lasted 38 minutes.
The Tri-State tornado lasted for 3 hours and 29 minutes.