Windows only: Setting (and re-setting, and re-setting) your camera's clock can be a pain, but wildly incorrect photo timestamps even more so. Here's a free program that can keep your shots in sync.
Back in the days of yesteryear, when everyone used film cameras, if your camera even supported a time function, the worst that would happen if you neglected it was the time stamp on the back of your photos would be off. Now, with photo applications to organise our photos and a reliance on the EXIF data to get that organisation done, having the wrong date and time on your photos means they get put in the wrong place and badly sorted in your collection.
EXIF Date Changer is a simple and free Windows application which allows you to alter the EXIF time stamp on your photos. You can alter the hour, minute, and second a photo or batch of photos was taken to synchronise them with the actual time or, more helpfully, with other cameras. I've found EXIF Date Changer to be invaluable for the times I've been using two cameras and forgotten to synchronise them to each other or have been at an event where multiple people are shooting and we all share our pictures. EXIF Date Changer makes it simple to synchronise photographs to the proper time and the output of individual cameras to each other. EXIF Date Changer is freeware, Windows only.
EXIF Date Changer [Relik Software]