The precise reply calls for preliminary traditions concerning various topics as follows:
First: Traditions that talk about signs and groundwork for Imam’s ‘Zuhoor’:
Once, the holy prophet (s.a.w.a.) addressed the attendants as follows:
“How would it be when your women turn lewd and your youth adulterers and you will forsake enjoining the good and forbidding the evil?”
The attendants said:
O messenger of Allah! Will such an incident ever occur?!
“Yes, even worse than this would occur! How you would be when good shall be presented as evil and evil as good….?” 
Also, Asbagh-ibn-Nubateh narrates from Amir-ul-Mu’mineen (a.s.):
“At the end of time and approach of the hour (resurrection or reappearance), [which is the worst of all times], women would come out devoid of clothes and decorated with various ornaments. People would be seen exiting from religion, entering into troubles, inclining towards lust, hastening towards pleasures, making lawful the unlawful and they would be the everlasting hell-dwellers.” 
Besides, the holy prophet (s.a.w.a.) said:
“A time would come when filling the stomach would become people’s aspiration and materialistic life their dignity. Women would become the direction to which people would turn to and money and wealth would become their religion. They are the worst of human-beings who possess no goodness before Allah.” 
Second: Traditions that strictly prohibit fixing the time of Reappearance (Zuhoor) and likens it to the Resurrection Day.
I approached Imam Baqir (a.s.) and asked: When will the Qaem Aale-Muhammad rise? He replied:“The same question was asked before Allah’s apostle who said: His rising is similar to the time of setting up of resurrection which will not occur but all of a sudden.” 
Similarly, Fuzail says:
I asked Imam Baqir (a.s.): Is the hour of ‘Zuhoor’ known? He replied:“Those who fix the time are liars; those who fix the time are liars; those who fix the time are liars.” 
Also, Imam Sadiq (a.s.) said:
“Those who fix the time are liars. We have neither fixed any time in the past nor shall do so in the future.” 
Third: Traditions that lay stress on invocations for hastening ‘Zuhoor’ and calling upon Allah for help. If invocations weren’t effective, the holy Imams (a.s.) wouldn’t have emphasised to such extent. Invocation is effective for any affair that is capable of delay or acceleration. In ‘Tauqeeh’ of Shaikh Ahmad-ibn-Ishaq, Hazrat Mahdi (a.t.f.s.) says:
“Close the door of useless queries and refrain from putting yourselves at pain. Suffice yourselves to the extent necessary. Furthermore, pray excessively for accelerating the ‘Faraj’ (deliverance) because your deliverance lies in this (i.e. excessive prayers).” 
Also, Imam Kazem (a.s.) prays as follows:
“O Allah, I swear by Your concealed Name……that You send salutations on Muhammad and Aale-Muhammad and make haste in ‘Faraj’ of the avenger and make his specified day reach fulfilment….” 
Fourth: Traditions stress that the work of ‘Zuhoor’ would be settled in one night, and Allah would permit him to rise.
Zaris Kenani says:
I heard Imam Sadiq (a.s.) saying:“In Saheb’ul-Amr (Imam Mahdi) there exists a similarity with Joseph and that is Allah would rectify his rise in one night.” 
Fifth: Traditions that talk about Bad’a’ (change of previous Divine Will, plan and beginning of something new). This change of destiny is explained by Imam Baqir (a.s.) as such:
“Allah has not been worshipped to such degree as (belief in) ‘Bad’a’; or Allah has not been honoured to such extent as considering ‘Bad’a for Him’.” 
Thus, the traditions come down from the immaculate ones (a.s.) have declared the matter of ‘Zuhoor’ and rise of Hazrat Mahdi (a.t.f.s) as a changeable affair.
From the above five groups of traditions, we can conclude as follows:
It is likely that the entire signs of ‘Zuhoor’ could be subject to ‘Bad’a’ (change) such that Allah would give permission for Hazrat’s rise without the occurrence of those signs. We should realize that the affair of ‘Zuhoor’ lies in Allah’s hands and does not depend on the decisive and definite occurrence of signs. As per Divine wisdom, this affair would be corrected in one night. Verily, our duty at this time is to create a sound creed (belief) and ethics at individual and social levels and before that to pray excessively for ‘Faraj’.