Mat 24:23 Then if any man shall say unto you, Lo, here [is] Christ, or there; believe [it] not.
Mat 24:24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if [it were] possible, they shall deceive the very elect.
Mat 24:25 Behold, I have told you before.
Mat 24:26 Wherefore if they shall say unto you, Behold, he is in the desert; go not forth: behold, [he is] in the secret chambers; believe [it] not.
Mat 24:27 For as the lightning cometh out of the east, and shineth even unto the west; so shall also the coming of the Son of man be.
Everyone will know at the same time when Christ has arrived. The bible says we should not believe anyone who has seen him before then.