I received a message while logged into xbox live on my xbox one, roughly 10:40PM (EST) on Nov 6, with a free $5 gift card code. Message is in the section "Messages from Xbox Live" while accessing the "Communication" tab on the Xbox one menu.
Message contents: "Enjoy a free $5 gift card on us to kick off your holiday shopping for that perfect gift. Redeem by November 30, 2017 and spend within 90 of redemption. See full terms at Microsoft.com/cardterms. *redemption code here*"
You can also access the message system by logging into Xbox.com, and going to your messages by clicking your profile icon in the top right corner (desktop browser).
It may also be possible that Microsoft is sending these out in staggered time frames and/or to targeted customers. As a note, I am a paid Xbox gold subscriber.