You really seem to be asking two different behavioral questions.
1. How long does it take to teach soft mouth and bite inhibition?
2. How do I teach my puppy calm behavior?
For the first one, it can take quite awhile. Keep in mind that at 4 months old they are starting to lose their baby teeth and get their adult teeth. Provide lots of good chew toys. Consistently practice the yelping when they bite and remember the 3 strikes rule, if they bite three times in one play session then it is time for a time out.
For the second one, there are lots of things you can do to start teaching your puppy impulse control and calm behavior. For impulse control, start playing the It Yer Choice game, http://www.youtube.com/watch?v=ipT5k1gaXhc For calm behavior, start making Down a requirement to get the things like food, a walk, etc. You can even measure out her dinner and instead of just putting the food bowl down. Have it near by when you are sitting down to watch TV for the evening and everytime you notice your puppy laying down toss her a treat. She should catch on that Down is what makes good things happen.