is 1-2 days delay normal for a menstruation?

Sex happened on the 21st day of her cycle based on the flo app. She is on a regular 28 day cycle and she should have her period by yesterday and still does not have it now. It was kind of unprotected but it only lasted around 3 mins and the guy definitely did not finished.

Do you think it is still safe from pregnancy or should we worry?