In general, the time that a movie stays in production is from a couple of months to about two years. The Other Side of the Wind (2018) holds the record for a movie to be in production for the longest time.
Here is a list of movies with at least 2,000 votes that took at least three years in production.
Which of these movies do you think was worth the wait?
Discuss the poll here
Source: List of films with longest production time