Autosave is a feature we’ve had for a while on the old post editor, and it does what you’d expect: automatically save your draft posts when you pause in your typing. We’ve brought the same convenience and safety to the new post editor.
With automatic date and time, your posts will now be timestamped with the date and time that they’re published, not the date and time when you first opened the post editor (as has been the case). You can of course still explicitly set the date and time by opening Post Options and switching to Scheduled at instead. Once a post is published, it will keep its date by default, even if you go back even if you go back to edit the post and re-publish.