Is It Safe To Take Northisterone On The First Day Of Period?

I was given Northisterone to delay my period as I am going on hoiday, I decided not to take it as I was due on four days before going, so I thought it would be ok as it would ony over lap by a couple of days, I was three days late so now it looks like I will be on over most of my holiday, is it ok to take Northisterone on the first day of your period?