In the first scene Sven is standing with four buckets (full of paint) hanging from his antlers. We see Elsa scolding Olaf for eating the cake for a few seconds, and then cut back to Sven: now the buckets have disappeared. It would be logical for Sven to have put them down at this point since Kristoff had just finished painting, but the buckets are nowhere to be seen on the ground or the tables, and Sven and Kristoff were standing too far from the entrance of the castle for either of them to have brought the buckets back inside in that short a time-frame.
The lighting and colors during the tower scene and the party at the castle suggests that the sun is going down. Some sources say that Anna's birthday is on the summer solstice. In Norway, which is the real-life Arendelle, the sun doesn't set for over 24 hours on the summer solstice (hence why it's called "The Land of the Midnight Sun"). However, this is only the case within the Arctic Circle, and we see both day and night in the original film, which would suggest that Arendelle is south of it. The Norwegian town of Arendal (which is the origin of the name Arendelle) is itself south of the Arctic Circle.