Yeah, that's a great question.
Listening, I think, is always a bit hard. Like, have you ever had trouble understanding someone from your own country? I have, plenty of times, whether it's an unusual accent or background noise or the person's not stating things clearly. Or maybe it's me and my mind's on vacation. Whatever. So what I mean is that I can go all week speaking nothing but Japanese at 100% comprehension, and then meet some random dude and not know what the hell he's saying. Like I spent last weekend with a bunch of farmers out in the country and probably understood 10 percent of what they were saying unless they specifically used standard Japanese for me. But then I've had similar experiences in the U.S. as well.
And I'll add this: listening also strange. You can go a long, long time and not know what the train announcements mean, and then one day, bam! you just understand them. I don't know why. You just somehow get used to the sound and then it makes sense. Of course, you have to know the words, but beyond that, you have to be able to assemble the sounds into something understandable. And that takes exposure.
So that's my roundabout way of getting to the point of saying, yes, watching subtitled movies helps, but . . . it doesn't help right away. It takes time. But as you continue studying, you'll notice you graaaaadually understand more and more of the dialog in movies (as well as other media).
I wouldn't make movies my main study method, but neither would I delay listening to them for too long, since they provide valuable, realistic dialog in context. Of course, you should probably pick movies with simple themes: love stories, household dramas, not some detective story with a complex plot and technical script.
So that's my long answer
Ken