I had the exact same issue yesterday. Last free entry was received at 4:22PM the day before, and I got that pesky error message of one spin per 24 hour period all the way to 11PM. I even wrote to support and here's what they answered (if it can help anyone).
Thanks for reaching out! You can claim one free spin every 24 hours. The free spin is not automatically sent to you every day, you need to go to
https://www.theory11.com/holiday/contest every 24 hours to claim each spin. Come back every day for another shot! Remember - every new spin you earn uses a NEW link, so any links you have to old spins don't do any good once you use the spins.
Spins are restricted to one per IP address per 24 hours. If you have friends or family members on the same internet connection trying to spin as well, you will need to use a different internet connection.
If the page is showing an error after the 24 hours are up, you may need to clear your cache/cookies on your browser and hard refresh the page; this should then make your spin available if you have waited 24 hours since your last spin.
Please let us know if we can be of any further assistance, and happy spinning!