This is the ruling of Ayatollah Sistani
Long-term stay (LTS) (watan al-itikhadhi): A place where a person plans to stay long-term for work, school, summer or spring vacations, or similar purposes, even if they do not own property or a home there. Except for the first month of stay during which time the person must perform both full and shortened prayers and fast the month of Ramadan and make up those fasts based on obligatory precaution if one of the following criteria related to their stay in that place applies:
o Remain there for six hours during every trip, in twenty-two days every month, for four years
o Remain there for eight hours during every trip, in twenty days every month, for four years.
o Remain there for twelve hours during every trip, in fifteen days every month, for five years.
o Remain there for twelve hours during every trip, in twenty-two days every month, for three years.
o Remain there for twenty-four hours during every trip, in seven to eight days every month, for four years.
o Remain there for twenty-four hours during every trip, in fifteen days every month, for three years.
o Remain there for twenty-four hours during every trip, in twenty-two to thirty days every month, for one and a half years.