The signs of the hour refer to the minor and major signs that would precede the day of Judgement. Belief in the day of Judgement is one of the articles of faith and is a requirement for a Muslim to believe in. The day of Judgement will fall on the day of Jumuah (Friday) and it’s exact timing is known only to Allah (swt).
“They ask thee about the Hour, ‘When will be its appointed time?’ Wherein art thou (concerned) with the declaration thereof? With thy Lord is the Limit fixed thereof. Thou art but a Warner for such as fear it. The Day they will see it, (it will be) as if they had tarried but a single evening, or (at most till) the following morn!”
Sura An-Naziat 79:42-46
However, all the prophets and messengers have warned their people of this great day, when all of creation will stand before the Master of the day of Judgement. Allah (swt) in his wisdom, has made known the signs that would precede the day of Judgment warning those who may take heed of it’s signs.