Nobody will know the exact time, but we are also told that the general time frame will be recognized by Christians:
1 Th 5:1-6 But of the times and the seasons, brethren, ye have no need that I write unto you. For yourselves know perfectly that the day of the Lord so cometh as a thief in the night. For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.
But ye, brethren, are not in darkness, that that day should overtake you as a thief. Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness. Therefore let us not sleep, as [do] others; but let us watch and be sober.
™ Version 4.2