by Eeeville
If you use the purple die part of the expansion, each player having an extra die every round will increase the play time.If you use the ramparts & guard part of the expansion, players will tend to use more actions with a single die since you can't group dice when doing a guard action.
Also, when using the ramparts & guard expansion, the West outdoor activity can bring back used dice to be used again.
All of these aspects can increase the play time. If you just use the new cards there should be no increase in play time. I personally don't like playing with the purple die. I do, however, play with the ramparts & guards and consider any extra play time to be worth it.