Indeed the time limit given for Muslims to establish a Khaleefah is two nights. So no Muslim is allowed to stay for more than two nights without having a Bay’ah on his neck. Making the upper limit as two nights is due to the fact that appointment of a Khaleefah is Fard from the moment the previous Khaleefah dies or is deposed. But it is allowed to delay the appointment while engaging in it for two nights. If the delay exceeded two nights and the Muslims did not establish a Khaleefah, the matter is examined. If the Muslims were busy in establishing a Khaleefah but could not complete it within two nights due to overwhelming matters they cannot resist, then the sin will drop from them because they were engaged in establishing the duty and they were forced to delay it by compelling power. The Prophet (saw) said: “The sin due to mistake, forgetfulness and compulsion is removed from my Ummah.” But if they were not engaged in performing the duty, then they would all be sinful until the Khaleefah is established and at that time the Fard will drop from them. But the sin they committed in neglecting the establishment of a Khaleefah does not drop from them, it rather remains on them, and Allah (swt) will bring them to account for it the same way He (swt) brings any Muslim to account for any disobedience he commits when he neglects to perform a duty.
In regard to the evidence concerning the two nights time limit given to Muslims to perform the duty of establishing a Khaleefah, it is an Ijma’a of the Sahabah. The Sahabah started to meet in the courtyard of Bani Sa’idah, to discuss the appointment of a successor to the Messenger of Allah (saw) as soon as the news of the death of the Prophet (saw) reached them. They kept discussing in the courtyard, and on the second day they gathered the people in the mosque in order that they might give the Bay’ah. This took two nights and three days. Also, when ‘Umar (r.a.) became certain that his death was imminent as a result of the stab wound, he entrusted the people of influence, the six remaining senior Sahabah, and gave them three days to choose a new Khaleefah. He ordered that if after the three days an agreement was not reached the one who disagreed should be killed. This was despite the fact that these were of the eminent Sahabah. ‘Umar (r.a.) also empowered fifty Muslims with swords to kill the one who disagreed. These orders were given in front of the Sahabah, and no one was reported to deny or disagree with it, so it becomes Ijma’a of the Sahabah that Muslims are not permitted to stay without a Khaleefah for more than two nights and three days, and the Ijma’a of the Sahabah is a legitimate Daleel Shari’i (evidence) like the Qur’an and Sunnah of the Messenger of Allah (saw).
Therefore, the re-establishment of the Khilafah is the most vital issue and the priority obligation for the Muslims. It was worth not only the lives of the Sahabah (ra) but also the Messenger (saw) was prepared to give up his life for the establishment of this Deen. He (saw) stated to his uncle concerning the Mushrikeen, “...by Allah, if they were to put the sun in my right hand and the moon in my left, on condition that I relinquish this matter, I would not relinquish it until Allah has made it dominant or I perish therein”. (Tareekh ut-Tabari by al-Tabari Vol. 6 par. 1179).
Hence the re-establishment of the Khilafah is the priority issue for the Islamic Ummah and the matter which will restore all the Faraa’id (obligations) of Islam and remove all the Munkaraat (evils) that are effecting the Islamic world and establish the Ma’roof (good).
Imam Shatibi has stated in his book Al-Muwafaqaat fee Usul il Ahkam (Vol. 1 Section 1 page 119-121) that the obligation of appointing an Imam falls upon those that are capable of establishing it and those who are capable of taking that position but if they do not appoint him then everyone else must work to ensure that those who are capable fulfil their obligation and hence it becomes a Wajib to work with those that are capable to resume the Imamah based upon the principle “Whatever is necessary to accomplish an obligation is in itself an obligation”.
Therefore it is an obligation upon every single Muslim today to work to remove the current systems in the Islamic lands in order to re-establish the Khilafah and bring Islam back to the Ummah.