What is the meaning of "a person fearing the expiration of the prayer time"? And does it refer to the strong probability of the time expiring due to a certain action, or merely the possibility of its expiration?

The meaning of fearing the passing of prayer time is that a person is certain or has a strong presumption that if he engages in work or sleeps after the time for prayer begins, he will not stand up or finish his work until after the time has ended, thus missing the prayer. Therefore, it is not permissible for a Muslim, after the prayer time has begun, to engage in work that he presumes will consume the entire time, or to sleep after the time has begun with the presumption that he will not wake up until after the time has ended. However, if he has a strong presumption that he will finish his work or wake up from his sleep before the time expires, then there is no harm in it.