For reference here are the screen time numbers per regular character in season two. For reference purposes Hook and Neal were included here despite the fact that they signed as regulars in the course of the season.
caption changed for the sake of accuracy
Please remember that screen time doesn’t necessarily reflect the importance of those characters to the story. Adam rightly points out that Darth Vader has very little screen time in the original Star Wars movie and Rumple only has a couple of minutes of screen time in the pilot.
Below the cut you will find episode by episode graphs.