People have been posting about problems with this competition all week. It seems, from reading various threads (although I'm not doing the competition myself), that you can't enter one day's answer unless you've already provided a correct answer for the previous day's clue.
The deadline for entering is meant to be 2359 on the day that the competition appears, so you've theoretically got just a minute or two left, but the content of your post suggests that the competition's clock is running fast for some reason, resulting in you seeing tomorrow's entry page. (Sorry!).