I don't. I just let it set out and mix for the 24 hours. room temperature (usually 72 degrees in my house) gets it close enough that it doesn't seem to affect the tank temp. as far as top offs go, I just poor it in the sump. even if it's pretty cold water. but, it's normally only a 1/2 gallon or so.
My room temperature(72-74 degrees) is close to my tank temperature(77-78 degrees) so no I don't heat the water.Having it close to your display is the safer way.
If you are doing a "normal" sized water change (10 to 20%), then the new water being slightly lower temp. than your tank isn't going to make a difference. For larger water changes it's more important to match the temp.