WordPress automatically saves revisions to your posts and pages every 60 seconds. You are able to modify decrease the time interval if you’d like to reduce the chance of losing changes or increase it to cut down on the load to your database.
You can change the autosave frequency by adding the one of the following lines to the site’s wp-config.php file.
/* Set AutoSave to 30 Seconds */ define ('AUTOSAVE_INTERVAL', 30);
/* Set AutoSave to 5 Minutes */ define ('AUTOSAVE_INTERVAL', 300);