As you are working in WordPress, something almost magical happens. WordPress will automatically save your work for you. So if something happens and your work gets lost, you can go back to the auto save and not have to start over from scratch. The default value is a minute, but that might not be right for you so to change the default time you will want to add the following code to the wp-config.php:
define( 'AUTOSAVE_INTERVAL', 40 );
Where the 40 is the seconds between auto save, you can change this to what ever value (in seconds) that you want.