The truth is, the author of this book doesn't know when the world will come to an end–and neither does anyone else. The Bible warns us against such speculations, and you should not take them seriously.
However, this book is correct about one point: Someday the world as we know it will come to an end. But it will happen only in God's time–and it will happen only when Christ returns to establish His perfect rule of peace and justice over the earth. When Jesus ascended into heaven after His resurrection, the angels told His watching disciples, "This same Jesus, who has been taken from you into heaven, will come back in the same way you have seen him go into heaven" (Acts 1:11).
While we aren't told exactly when Christ will come again, we are warned to be ready for His coming. What difference would it make in your life if you knew beyond a shadow of a doubt that Christ would come back tomorrow? I suspect it would make a big difference, and you'd do everything you could to be sure you were prepared for that day. You also would do all you could to warn others.
But why should it make any difference? We should be living for Christ every minute of the day–whether He comes tomorrow or in a thousand years. Make sure of your commitment to Christ, and then make it your goal to "pursue righteousness, godliness, faith, love, endurance and gentleness" (1 Timothy 6:11).