At first I thought this movie had a weak ending too, then realized that climax of the movie would get lost if they continued anymore. I am guessing that if they continued on with the next day, it would feel like a build up all over again. We might be waiting around for something big to happen that would end up being less suspenseful then the actual climax. If we think about it this way, the main character's relationship with some others would probably get awkward and perhaps boring. At the same time, closer with another character. In essences, it would be un-climatic and a general disappointment. I believe that's why the director decided to end it there, giving the audience the benefit of envisioning the ending.
The movie as a whole I thought was good. Needed some minor acting adjustments here and there, but had real aspects to it. Which I felt over shadowed those minor issues.