If it were me, Id send him a message and ask if he has put it in the mail. Like "Who" said, it can take 12 to over 24 hours for the updates.
Sometimes the persons printer doesnt scan and it has to be entered by hand and postal people get lazy and then you get a out for delivery notice or it just shows up.
If you specifically needed it by the date, I dont see any harm in a friendly " did it go out yet?" email especially if it is coming first class. The 17th is just a couple days from now and if its first class, and across the US it might not get here on time.
Oh, you did not specify when you got the label created notice. If it was a couple days ago, I definitely contact the seller if its a time sensitive item.