Why can a conditional change truth value in Philo of Megara’s theory?

In the history of logic, Philo of Megara defined a conditional proposition as true if and only if it does not currently have a true antecedent and a false consequent. This interpretation is equivalent to the modern concept of material implication.12

Because Philo’s definition relies strictly on the present truth values of the antecedent and the consequent, a conditional can change its truth value over time as the truth values of its component propositions shift. This contrasts with the view held by his teacher, Diodorus Cronus, who argued that a conditional is true only if it is impossible for the antecedent to be true and the consequent to be false at any time (past, present, or future), meaning a true conditional for Diodorus remains true eternally.12