I'm going off a beat sheet here and it says "The Bad Guys close in" happens right after the mid point. Thing is, I don't want to make them too much of the focus and I should sprinkle some character bits here and there prior to that so they don't come across as "oh, we never knew that before" parts. Basically I'm doing a chase thing; think the Fugitive. The "villain" is a group of 4 soldiers chasing the heroes. One suffers from split personalities and wants the others in his head gone. One is a doctor helping the previous but withholding said character's secrets and in a sort of "do you really love me or is that just your job" situation. The 3rd is a comical guy who's just the buddy. The 4th is the real big bad villain because the other villains are sympathetic and pretty much turn face. Now, I can probably spare them 2 scenes in act 1 leading into act 2. 1 in Act 2 part 1, and then...4 in act 2 part 2, leading into act 3. See, I worried that last chunk is too much.
A character is a character. Some require more thought and shaping than others, but this has nothing to do with whether they wear a white hat or a black hat. Or both.
Each type of character is going to require a different type of care, sort of like a child. A brain child. A brain child who may or may not slay dragons/be a dragon haha. Really though, your villain is often going to be the second or third most important character in your work. Good villains are often to some degree a sympathetic figure. Its the fact that we identify with the evil in the villain that makes us despise him/her all the more. You want to give the villain just enough face time to show that he is a person while not allowing him to fall into a sort of anti-hero role. That is a very thin line most of the time. When it comes down to it, write it how it feels. If you get to a point in your editing and realize that from a reader's standpoint they would know nothing of your antagonist, he probably needs more face time. If you read through and find you are skipping through straight to portions containing the villain because you like them better, it could probably benefit from revision.
Villains go through periods of evolution. Many famous villains are the way they are today because of some small changes that the author made along the way, years later. It all depends. Think of a cool costume, though. I don't care how interesting the story is, a good costume not only complements it, but without it, the story is incredibly boring.
The only answer is as long as it takes until you feel the character is developed enough but any character will continually develop as you are writing your story.
Actually, your "villain" is AS important as your hero. Imagine, if you will, Batman without The Joker (or any of his other arch rivals), he'd just be some wierd guy running around town in a cape and tights and a possible pedophile living with a young boy! Your protagonist needs a foil, someone or something to work against in order to achieve his goal or conquer his foe. If he doesn't have that someone/thing to fight against, he's ... just another guy on the street. Nothing exciting. Why care about him? Sure you can write a novel/play/movie with a lackluster villain. But you would probably just creat a lackluster piece. Black and White. Good and Evil. It's the Yin and the Yang. You can't have one without the other.
