This might sound like a very silly question, but I'm in search of an ultra-short Scarlatti sonata. I'm afraid I might have passed my 30 min limit for a first round of a competition program, and I would be able to switch my Scarlatti sonata for another one, which seems like a decent option.

Either this, or I'll play the Hammerklavier 1st movement at 138 on the half-note

Perhaps just play the Scarlatti you already have already prepared without repeats.

I'm assuming you aren't timing things to within a few seconds, so there are probably at least 50 Scarlatti Sonatas within less than a minute of the shortest one(even when played with the repeats).

K. 431 on my iPod clocks in at 44 seconds.

Is that short enough?

I agree with Copake. I have heard that K431 is the shortest sonata by Scarlatti before.

As a more general thing: It's an awful idea to be approaching a competition with any concern about needing to stay under a time limit because you're skating on the edge. (I know, because I failed to heed this well enough last month and paid a price.)

Whatever you do, I'd suggest you make sure your program is comfortably enough within the limit that you won't have any concern about it anywhere in your mind when you get up there. It sounds like you might be in danger of skating on an edge like that. If it's possible to do what Plover suggested i.e. omitting a repeat, either with Scarlatti or another piece and if that's the best way to give yourself some margin, it might be a good idea.

Thanks for advices on Scarlatti and other words of wisdom. At this point, it doesn't matter too much if I'd play the Scarlatti that currently is in my program or another one, because I haven't worked for a minute on Scarlatti yet It's an interesting feeling, realizing close to a competition that you've put too many new (or way old and thus forgotten) pieces on the program, and that it'd be nice to have a few more extra weeks. The Scarlatti is the last new piece though and everything else has been publicly performed (and rather recently, with the exception of the Prok 3rd concerto). My current Scarlatti would be about 2 minutes I believe - K 431 does seem like a perfect substitute, and a better option than skipping the so important repeat in Hammerklavier 1st movement. Has a single note ever been so important for the structure of a piece...? I played it without repeat in a masterclass, and a cellist approached me afterwards, saying: "You only skipped the repeat since it was a masterclass I hope?"

You could respond, as Brahms did, that when the piece was new and nobody knew it, you had to play the repeat, but now that everyone knows it, that is no longer the case. I would think that for the purposes of a competition, where the goal is to prove that you can play well, repeats could be omitted. If you win the competition and get a recital, you can play the repeat then.