it is my opinion that water changes can be very taxing on the inhabitants of ones tank. Although there is no prescribed schedule or agenda when to comes to WC's , there are some basic practices that can reduce the shock of WC's on your system.
I usually mix my water a couple of days ahead of time and keep it circulated and well saturated with O2. Then test the parameters in the display and then test your new water. The big three things you want to match are temp, ph, and salinity. Although it may be noted that you may wish to test for other parameters as well such as Alk, Calcium, or even mag. Once you've matched ypur parameter's you should be good to go.
Personally I like to do my WC's either when the lights are out or just the acintics being on. I will siphon out of the display and fill into the sump.
One last thing, and opions will vary on this, is the amount of the change and the frequency. Some people like doing biweekly or monthly changes, and any of these are okay as long as your fairly regular about it. I prefer to do a 5 gallon change every couple of days, and my reasons are for this... IT IS MUCH MORE STABLE WATER CONDITIONS. Your constantly taking a little and giving a little is never so bad as your corals adjusting to bad water and shocking them with a large change.