The EXIF data hold a lot of useful technical information about your photos. One of these is the date and hour of the snapshot. This is quite pleasant, useful and nice up to the moment when your camera internal clock fails or starts lagging. Or when you need very precise synchronization with another device (like a GPS geo-marker, for example). Here, you need to correct precisely the hour (or worse, the date) written in your photos and -generally- you have to do it on dozens of photos at once.
How to do this? Under Windows, ask to EXIF Date Changer from Relik Software. This utility program will allow to correct this information in a matter of seconds.