It took my plaque only a day or two to arrive. When I picked up the mail, it appeared in my sim's inventory. But check your collections notebook to make sure that all four wreaths are shown as collected. It seems that sometimes collections get glitched. This post gives suggestions for workarounds in case of problems:
Thanks, the incomplete collection was indeed the problem. I found out by accident when I took down the Christmas decoration and put the new wreath into the household inventory with the others. That triggered a pop up message informing me that I had received a nice plaque. All I have to do now is pick up the mail.
