I think movies can be very good in the classroom (some that I've used include Big, The Mighty Freak, Princess Bride) but like anything, they can be abused.
It isn't a question of the amount of time. It is a question HOW you do it.
I'd consider breaking up the movie into scenes and having activities associated with each scene. This can be as easy as one partner watching, another describing - listening for vocabulary or retelling. Or it can be more expansive with activities about comprehension, what if...., prediction (the most beneficial for books or movies) and just spin off activities.
But break it up. You can see an example at my resource site. What I did with the movie
BIG. Answer key in that same folder and we often discuss movies being used at EFL Classroom 2.0.
Hope this helps.
David