In the movie most of the events of Harry's two visits to Hogsmeade are rolled into one just before Christmas, when he and Ron are still talking to Hermione - essentially his throwing snowballs at Draco is added, though, differing to the book, in the movie his cloak never slips off his head so Draco doesn't run off screaming to tell Professor Snape. This latter incident in the book is where Snape sees the map, Lupin gets involved (as DADA teacher) gets involved since Snape thinks the map is the work of dark wizards - Lupin confiscates it.
Of course they needed to get that scene in somehow, so they have it late at night when students are meant to be in bed, Harry looking on the map to see Peter Pettigrew running around the corridors. Harry slips out of bed, and the Snape/Map / Lupin scene plays out then. A scene that isn't in the books, but given that the film makers have to consult JK Rowling on changes I guess it can't detract from the main plot of the movie. | 
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