I want to make the sentences appear slowly instead of all at once when another option is clicked. Is there a way to time its reveal of each sentence so that I can make dialogue appear different from the normal text?

The @replace function causes new text to appear rather slowly in place of old text. Other than that, I don't think there's anything in Squiffy itself to "time" things.

http://docs.textadventures.co.uk/squiffy/replace.html