Exif Farm - how to edit date and time
1. Right-click selected files* and choose "Properties" from the context menu:

2. Select the "Exif Farm" tab in the opened window and click "Edit Exif data":

3. The following window will appear:

4. Click the "Edit" button to edit date and time:

5. The following window will appear:

To set new date, edit the following field:

To set new time, edit the following field:

Please note that the time is used in 24 hour format. This means, if you want to change time to 3 PM, you need to add 12 hours to the "PM" time: 3+12=15. So, you need to enter "15:00:00".
To add several days to current date, use the following field:

First, activate the radio button of this field. To set timestamps (you can also do it to several photos*) for example, 2 days ahead, enter "2":

To add several hours to current time, use the following field:

First, activate the radio button of this field. To set timestamps for example, 7 hours ahead, set the value to 07:00:00:

To subtract several days from current date, use the following field:

First, activate the radio button of this field. To set timestamps (you can also do it to several photos*) for example, 2 days back, enter "2":

To subtract several hours from current time, use the following field:

First, activate the radio button of this field. To set timestamps for example, 7 hours back, set the value to 07:00:00:

6. Click Save.
* Batch editing is available in the registered version only.