Best I can guess there is some clash going on with the datepicker. Maybe the cause is that the Hours extension uses an addon for datepicker called timepicker. If that is the case, there’s really nothing I can do to fix this.
Ideally, the other plugins would limit their scripts to the pages that they are needed like Hours does in order to precisely limit/prevent conflicts like this.
Sorry, I do not have a better answer for you!