Hello I Want To Use Norethisterone To Delay My Next

Hello I want to use norethisterone to delay my next period . I never know the exact date to predict my period but it usually comes about a week earlier than the previous months date . It says to take the tablet 3 days before your period is due. Because I don’t know the exact date , is it bad to take the tablet about a week before it is due to ensure you don’t miss it