Thanks for query,
The pills taken after 50 hours of sex may or may not work.As such it should be taken before 72 hours of sex but it is not exactly a time line.it depend upon the hormonal
level you acheived in your blood & its concentration in different individual is different from case to case.
As you have sex on last phase of late cycle but the chances of being pregnant is very less but there were possibility of it.
So Don't worry just wait for next period to come.