Meh. I really hope that I will get it before the estimated delivery date.. Someone had the same delivery date (Dec 21-Jan 3) and theirs has been shipped on Friday with a estimated delivery date of Dec 22 so I guess it's possible that i'll get it before Dec 27 but there's no way that I get it on Dec 21.
You never know it could suddenly change but the 21st might be a bit ambitious! I hope you do get it sooner though, don't rule it out