This page used to be much longer. Who has time today to read a bunch of tips? So here it is in a nutshell:
Do not try to time delivery to a particular event. Things happen. Also, the return period starts when the item is delivered to the address you specify, not when your recipient receives the item. So, for example, if you take delivery on 15NOV and try to return it on 27DEC you're out of luck. Surprise gifts aren't always the best way to go.