Hi There My Daughter Has Be Advised To Take Utovlan

Hi there my daughter has be advised to take Utovlan to delay her period whilst we are on holiday next week, she was told to start taking the tablets 2-3 days prior to her period starting. The trouble is my daughter has irregular periods so we are unable to pin point the exact date she is due. We fly next wed so would it be OK to just start the tablets on the Monday before we go and Hope they work or is this too dangerous?
Many thanks.