I've been a good sportsmen

so far this season and released some decent fish. If I do decide to keep a large I was thinking of entering it into the Cup for S-B but I'm currently not entered.
I was checking out the rules and found this:
• A competitor must be registered in the tournament 1 DAY BEFORE commencing to fish.
I'm taking this to mean that if I drop a slob and register before midnight and then weigh it in in the morning it's "legal fish".
or
Do I have to register one day, then wait another day and then I can weigh it in the day after that?
Correct interpretation?