Although I didn't write the movements in order, I did save the fourth movement for last. I knew I wanted it to be a rondo, with the contrasting sections quoting the other movements. So they had to be completed first.
With all four movements complete, the estimated playing time for this work is about 7-8 minutes. It could run a little longer if tempos are taken slower -- and that would be fine. I'm more concerned with a clear contrast between slow and fast than a strict adherence to a metronome marking.
I'm not entirely happy with the coda. I might rewrite it as part of the editing process. But overall, I think the music came out pretty much as I heard it.
And for reference, here's the original Diabelli Project sketch for this movement (No. 148).