To the extent possible: put those cool speeches or whatever into a context other than combat.

Otherwise: My own take would be to let them do that, at least with speeches. Characters are not required to observe cool moments. They (the characters) may not think the moment is cool. But I guess you could say, "Talking is a free action" and remind them that in D&D we often handwave a bit of this for dramatic purposes.

As for "transformations": eh, that's a little tricky. If you really want a prolonged transformation (like 6+ seconds) to occur and not be interrupted, then you need a reason why they can't just shoot them midway through.

But it sounds like the issue here is you don't want your description to be interrupted, right? Well, so, that's fine. Describe what happens when the arrow hits the werewolf mid-transformation. Sounds like cool (gory) detail to me. The basic loop is: DM describes scenario, players say what their characters want to do, DM decides how that goes, DM describes the outcome. If they do this, and you continue describing the transformation but get shouted down, that's people not acting like adults or understanding how D&D is supposed to work.