Denny’s is one of the major chain restaurants that is open all year round and it is generally open 24 hours a day. This means they will be open on Thanksgiving. However, this is at participating locations, many of which may be incorporating a holiday schedule. But, if you do not want to contact the restaurant directly, you should be safe going until early afternoon at least. As for IHOP, they should be open as well. And, the holiday hours vary among the locations, so be sure to check with your local store.