Several hundred years at least (see my sibling comment). And in all likelihood this will be handled by shifting the time zones by an hour, or possibly by omitting one DST adjustment in spring.
In the very far future, leap seconds would become inadequate anyway, as you’d have to insert them every month, then every week, then every day, due to the deceleration of Earth’s rotation.
In the very far future, leap seconds would become inadequate anyway, as you’d have to insert them every month, then every week, then every day, due to the deceleration of Earth’s rotation.