Since 4.1 there is an AutoSave options
Help mentions it here:
But actually it's in the expert configuration since LibreOffice .. ?
Note: Which leads to the idea (maybe already decided sometime) that options that have been moved/are added in Expert Configuration, do have a help text that resides with the Help for related not hidden features.
Actually it is also in the UI, but hidden as per bug 65509 and http://cgit.freedesktop.org/libreoffice/core/commit/?id=4653c91a89cfe802754377bcdafc291526254a03
because the button for "userautosave" to automatically save the document also (in addition to autorecovery) apparently was not work correctly.