It differs from person to person of course, however studying 5 days a week for 3 months while living in Japan should enable you to be able to engage in basic daily conversations and do things such as buy goods and order at restaurants.
After 1 year you will be able to explain what you need in places such as hospitals, banks, and city hall.
In addition to acquiring conversation skills, many students are able to pass the N3 or N2 after one year, and the N2 or N1 after two years.