some will tell you to carb deplete for up to seven days, ( I prefer about five) and some may tell you to load for four (I prefer about 2 and a half). Your bodies response to carbs is best known by you alone, do you get a good pump after a high carb meal, and how many carbs do you need to achieve the good pump.
The best thing is to trial a couple of times when you are well out from contest time, so it doesn't adversly affect your diet. When loading a good rule is to sip water with carbs on the last day when you may be cutting water from your intake.
I once carbed up only 24 hours and had no response and felt flat, tired, and weak onstage, it had no adverse effect on my details but had no positive effect either.
If you can track down a book called "shredded" by Negrita Jade and Bill Dobbins it is very good for pre contest. It is about ten years old so some supplement info is out of date but the pre contest info for the final week is priceless.
Good luck