It may interrupt the continuous flow of time without neglecting the conditions of the dramatic art.
There may be twenty years between the third and the fourth act, inasmuch as the dramatic writer must select those elements spread over space and time which are significant for the development of his story.

But he is bound by the fundamental principle of real time, that it can move only forward and not backward.

Whatever the theater shows us now must come later in the story than that which it showed us in any previous moment.
The strict classical demand for complete unity of time does not fit every drama, but a drama would give up its mission if it told us in the third act something which happened before the second act.

Of course, there may be a play within a play, and the players on the stage which is set on the stage may play events of old Roman history before the king of France.

But this is an enclosure of the past in the present, which corresponds exactly to the actual order of events.