Your camera wasn't adjusted to the right time and you now found yourself with many photos with erroneous info, here's how tho adjust the time and date at which your pics where taken.
- Open Picasa and select the photo you wish to modify.
- Click the Tools menu and then click Adjust Date and Time.
- Simply select a new date and time of the first and validate with OK.
- You can perform this manipulation with multiple of photos at the same time (batch operation).