Exif Farm - how to batch-edit EXIF data for a group of files
1. Select the files whose EXIF data you want to edit.
2. Right-click selected files and choose "Properties" from the context menu:

3. Select the "Exif Farm" tab at the top of opened window and click "Edit Exif data" way down the window:

4. The following window will appear:

5. Add required data to the fields, for example:

6. Click Save. In this case the options you have edited become the same new instead of previous for all selected files.
7. To edit date and time click the "Edit" button next to requested option:

The following window will appear:

Please pay attention to the time 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".
Further there are two ways of editing date (time).
The first way is to set new date (time). Note, the fields you are editing this way will become the same for all selected files.
The second way is to add (or subtract) any days and (or) time to current date (time). Note, in this case the edited fields will not be the same for each of selected files if there was any difference before editing.
7.1 To set new date, edit the left field of the "Set up new (date / time)" option, to set new time, edit the right field of the option:

Click here to get more detailed information on what field do you need to choose for date / time editing.
For example, you have selected two files with the date (time) values:

Say, you set the following date and time:

As a result you will get the same date / time fields at both of the selected files:

7.2 To add several days (hours) to current date, use the "Add to current time (days / hh:mm:ss)" field.
To subtract several days (hours) from current date, use the "Subtract to current time (days / hh:mm:ss)" field.
First, activate the radio button of a suitable field. Set timestamps for example, 2 days ,1 hour and 10 minutes ahead and click the "Ok" button:

Then click Save:

In this case the days (time) will be added to the current dates (time) of the selected files. The date (time) of each selected file will be altered by the value you have set. So these fields will become not the same as before:

To avoid undesirable change of EXIF data, please, make backup copies of files before editing.