WordPress automatically saves your post drafts after every sixty seconds, the feature is very useful for all bloggers because it helps you to get your content back in case your web browser crashes, your system hangs or shuts down etc. This tutorial explains you how you can change the default autosave time interval of WordPress from 60 seconds to something else.
Open you site’s wp-config.php file (present in the root directory of your WordPress site) and add the following line of code changing 90 to number of seconds you want for auto save time interval:
define( 'AUTOSAVE_INTERVAL', 90 );