Have you ever taken a bunch of photos with your digital camera, only to realize afterwards that the time set on your camera is incorrect? This is common if you forget to adjust the camera’s time to account for Daylight Savings Time or if you travel to different time zones.
This happened to me before and while I could edit the timestamps of the photos one by one, I had hundreds of them to edit and doing so one by one would be tedious and time consuming. Simply batch editing the properties of the images wouldn’t work since that would make all the timestamps identical.
Fortunately, it turns out Microsoft’s own Windows Live Photo Gallery provides a feature to batch edit the date and time of photos by shifting the time a certain amount. The instructions written here are for Windows Live Photo Gallery 15.4.
Simply select all the photos you wish to batch edit the timestamps of. In the top ribbon, head to Edit > Adjust time.

Click Adjust time in the ribbon
In the window that appears, simply adjust the time shown. The date and time shown is that of the first photo selected, but the remaining photos will be adjusted relative to the time indicated. So if you adjust the time from 6:00 PM to 5:00 PM, all the selected photos will have their times adjusted backwards one hour.

Change Time Taken
You will notice that the timestamps have all properly shifted. However, Windows Live Photo Gallery doesn’t actually update the metadata of the photo, so if you move the file to a different system or use a different program, the timestamp would still be incorrect.
To force it to update, apply an effect to the photos. You can choose any effect at all. After all the changes have been applied and saved, click Revert to Original and allow changes to save again. Reverting does not revert the timestamp, but does force Photo Gallery to save the photos.

Apply any effect and revert to apply timestamp changes
Have another method to batch edit the date and time of photos or another tip to share? Share with us in the comments.
Updated on August 21, 2012: Thanks commenter Frank for pointing out that WLPG doesn’t update the file itself.