Mahdis are the signs of the hour

Know also: that the Mahdis are the signs of the hour and its appointed time, with the last one the physical world ends, and the world of the Return (Rajaa) begins then the Day of Judgement.

The world of Return

{Al-Qasas (28):70){He is the Judgement}: meaning the sovereignty of Allah by the rule of Imam Al-Mahdi (pbuh), and the Mahdies (pbut) then the Rajaa (the world of Return), and the rule is for the Prophets and the Messengers and the Imams and successors.