The time it takes for any coral, not just Elegance, to fully acclimate and adjust to light is usually between several weeks to several months. It is a slow process. The coral comes into the hobby already "programmed" to a specific light intensity and schedule. The zooxanthellae (brown color) are set at a certain density relative to the light and the fluorescent proteins (bright color) are also set at a certain density relative to the light. When there is a large contrast between the natural environment and the captive environment it can have very negative effects on the coral, which cause negative behaviors; such as puffing, tentacle retraction, fading, bleaching, burning, prolonged tentacle retraction, algae invasion under the tissue, infection, and more. A coral will normally have to adjust to lighting changes that are barely even perceptible and the only way to show that these changes take place is by taking photos over a period of time. The point is that every change you make, even very small changes, are sensed by the coral and can affect the coral before it has time to acclimate because the acclimation process is SLOW. Therefore, changes must be made slowly.
The most widespread and deadly problem in this hobby is IMPATIENCE.