Callahan has never played 24 minutes per game. Ever. His highest for a season is 21:30, and that's this past season. Bumping him down, even if it's 2 total minutes to 19 minutes, is a downgrade for a guy who is one of your best players. I fail to see, by the way, how if your first and second line wingers are eating up 20-23 minutes per game Callahan is still going to be playing 20 minutes. Simple math shows that's not possible.
If AV wants to have a 3rd line that's purely defensive, then have your 4th act as a limited-role scoring line.
Hagelin-Stepan-Nash
Richards-Brassard-Callahan
Moore-Boyle-Fast
Pouliot-Miller-MZA
Pyatt/Dorsett
Obviously this is dependent on how MZA plays during his shot at the top 6. If he tears it up and Richards looks like garbage, have Richards center that 4th line and keep MZA in the top 6. There's a lot you can do with this roster, but cutting Ryan Callahan's minutes isn't something we should be discussing.