Yes you can have the pill within 72 hours of the act.

Though the chances of attaining pregnancy as per what u have wrote is very less But don't forget , precum also have sperms, whereas it also depends on the day of your menstrual cycle . And as I can understand , you guys don't want to take chance , so it's better to consult and take correct action rather then regretting later . Don't worry ,u will be helped .consult me.