And he (the dying man) will think that it is the hour of parting.
He knows it is the end.
and when he thinks it is the time of departur
And he is sure that it is the parting
And (he) thought/assumed that it is the separation
Then man knows that it is time to leave
And he will realise that this is the parting
And he is sure that it is the parting
And (the departing soul) comes to realize that (now) is the hour of parting (with all)
And he himself realizes that it is the (time of) parting
And he (the dying person) will conclude that it was (the time) of departing (death)