I made a reservation for the 19th till the 22nd due to my flight arrangements. I decided to call yesterday to see if I could add on an early check-in on the 19th because my flight lands at 10 AM and I figured it would make everything a bit easier as sessions start early on Monday. They told me they had cancelled the Sunday reservation as the hotel block was only for the 20-22nd!
They were able to solidify an extension, but I highly recommend calling and confirming your accommodations.