Holidays/Weather or not, it isn't right. If you're paid, ship right away.
I'm up front with people. I tell you ahead of time when I'm going to be able to ship.
If I don't get it out the day I say I will(which is rare), I'll say hey, I had this going on so I didn't ship. It will go out tomorrow.
I ship within 24 hours. There's no excuse not to. If you have the time to list items for sale, you have a spare 4 minutes to stick a label on a bubble mailer.
Just leave negative feedback. Maybe it'll change the way people handle their business.