I did some research online. Saw a lot of videos on youtube about end times. My research shows that end times are near. I want to ask your opinion on this matter. How soon do you think will Imam Mahdi will come?

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No one can place a definite time on when the Imam (as) will make himself known to the public. All we can do is pray for the hastening of his reappearance and prepare ourselves by striving to be the best servants of Allah that we can be.
Here is a book about the signs of reappearance

https://www.amazon.com/al-Mahdis-Reappearance-Sheikh-al-Din-al-Sagheer/dp/1976265231