The only way this can work is if the person sent back in time either has an amazing memory, or a photographic record of the position of the night sky.
The positions of the stars and the orbits of the planets work as a sort of long term celestial clock, and if you were to wake up one night and look out at the night sky and realize that the Moon, Jupiter or Venus were not in the "correct" positions, then you would realize that you are "out of time".
This is easiest to do if there is some sort of major astronomical event, such as a planetary conjunction (i.e. several planets appear close together in the night sky), a lunar or solar eclipse, or more rare, a comet.
OF course just because "you" know that the planetary conjunction you are looking at took place in year "x", "y" number of years before or after your arrival, sin't going to prove much. An astronomer can reasonably predict when certain astronomical events like eclipses and conjunctions take place and where in the night sky they are visible, so saying you are from 5 years in the future isn't going to cut it. IF you have an accurate picture of the night sky with a time stamp on your cell phone or camera, then you can make a stronger case, but since things can be Photoshopped, you will have a hard time proving your bona fides.