Placement of duration complement 很长时间 before a negated verb 没看?
Q1: Why is it located before the verb when duration should go after the verb?

The explanation you posted in your comment is correct. Reposting it here for clarity: when expressing the duration of an inaction, the duration complement goes before the verb, following the pattern:
Duration + 没 + Verb + 了

Q2: Does the final 了 indicate a change of status suggesting the speaker wants to watch a movie soon?

No, it indicates the change of status that occurred when you started not doing something.
In your example, it's the change from watching movies to not watching movies.