Hello, I Was Recently Adviced By A Doctor To Start

Hello, I was recently adviced by a doctor to start the duphaston pill in order to regulate my period. She told me to start the pills on the 20th day after I saw period and take the pill for 5 days.After I will stop it i must see period within 3-5 days. However I need to see period later this month since I am going to swimming competition. Can I take the pill for 6-7 days?