Rose water is typically a subtle flavor in a recipe. I love the complexity and nuance it adds, but the recipe is great without it.
I add a bit of alcohol to all of my frozen desserts as it lowers the melting point, and makes it more scoopable. In this recipe, it doesn't add much in the way of flavor, and is totally optional.
I received a bottle of Rose and Hibiscus Flower Extract at the Mediavine Bloggers Conference in April. I love it! I put a few drops on my scoops mostly for visual impact. Again, this is optional.
Time varies according to your appliance and how cold the mixture is going into it!