If you switch it around you'll get a notice because the IF evaluates
from left to right. So you just want to make sure you check isset() first.
This would throw a notice:
if($_POST['UserWishesDateRange'] == 'T' &&
isset($_POST['UserWishesDateRange'])) {
Aha! That must be what I tried and was still getting the notice! Interesting that it works (without notice) if we check against the isset () one first. It makes if() look more intelligent that I would think... as if it saying, "good now that we've established that the var isset, now is it also equal to '___'., as opposed to just, "is var set, and is var equal to "___'.