Digital cameras often tag photos with the date and time they were taken. Normally this works well, but if the camera clock is wrong then all your images will be out of sync.
If you're looking at hundreds of mislabelled photos then it may seem a big problem, but there's actually a simple solution. Open all the affected images in EXIF ReGenerate, then find and set the correct time for a single photo. Click an "Apply to All" button and the program applies that same time offset to all the other images - adding or subtracting x days, hours, minutes and seconds - and so bringing them back into line.
The EXIF ReGenerate interface is bizarre. For some reason the developer has decided to display your selected images in a fixed-size vertical stack, and we could see only the first six of our test photos. The others were only visible by scrolling, and you can't maximise or resize the window to get around this.
The workflow is odd, too. We chose an image, clicked "Set", gave it a new time, clicked "Adjust"... And apparently nothing changed, even that photo still had its original time displayed. In the background EXIF ReGenerate has calculated an offset, though, so if you next click "Apply All" (the green tick icon in the toolbar) all your other photos will have their "time taken" tags updated. (The file system dates remain the same, though, and file names containing the date and time won't be modified, either.)
EXIF ReGenerate has a poor interface, but it does work, and the program can update the times for hundreds of photos in just a few seconds.