Time frame is kind of hard to put on the "training" of corals as some corals will not conform. Certain non-photosynthetic corals can be "trained" to stay open throughout the day just by having food constistantly in the water column (gorgonians, tubastrea). For example, take a healthy tubastrea (feeds well, normally opens up at night), with the lights on, add Reef Nutrition Arctic-Pods or Argent Cyclop-eeze to the tank, them come back within 20-30 minutes. You will notice that your close tubastrea is open or partially open. At that point you can feed them mysis or LPS+ pellets. Do this often and they will stay open more often.
Another way to get them to open, shut the flow down to the tank, place LPS+ pellets on the closed polyps, wait a few for the polyps to take in the pellets before you turn the flow back up. That method works well too.
The hardest trick is to keep everything open all the time, especially when you want to take pictures.
Mike