You want to Post/Schedule multiple Photos either to an existing Album or to the Wall?
You can do that with Publer!
You don't have to create a new Album every time you want to post multiple images. After selecting the Social Accounts that you want to Post to, click the Photo Album Multi-Photo tab and click the green button "Select an existing Album" (if not already clicked). You will be able to select an existing Album for each Social Account that you selected. You can always switch between creating new Albums, posting to existing Albums and multi-photo posts.
You can upload more than one Image at once either from your local device or directly from external URLs. Keep in mind that you can upload up to 50 photos at a time. Publish your Post right away or Schedule it for a specific time in the future.
Don't delete the existing Album you selected from Facebook, otherwise your scheduled photos will fail.
Update (August 25th, 2016)
You can now select the Timeline Photos / The Wall as the existing Album. When doing so, your post will become a multi-photo post.