I need help.

I received my I-512L- Authorization for parole of an Alien into the United States.
It says date issued 11/25/15. I'm not showing how my days I'm allow to stay out side the us until I can return.

The letter says:
"Presentation of the original of this document prior to 12/20/15 allows a customs and border protection (CBP) inspector at a port of entry to parole the named bearer..."

So, I have from now to 12/20/15 to travel? 12/20/15 is my due entry date?
Anytime after this date I won't be able to enter???


Also, I only request one week bu I'm not showing any number of days available??

Please help.