Some suggestions:
Andrew Violette's Two Sonatinas (one or both)
Ursula Mamlok's Three Bagatelles (don't remember the exact length)
One of Roger Sessions' 5 pieces (they range from 2:30 - 4:00)
Some of Per Norgard's works for piano might be cool to check out, though they are not the easiest items to find recordings of. His op. 25b studies might make for some impressive performance material. Here's a link to his catalogue for piano at EWH:
https://en.ewh.dk/Default.aspx?TabId=2449&State_2955=3&ComposerID_2955=1141&CategoryID_2955=27Not
as modern as my other suggestions, but I'll almost always suggest Tansman's pieces, which are often polytonal enough to sound border-line dodecaphonic but simultaneously heavily accessible (to the audience and player) in terms of rhythm and melody. Any of his transcendental etudes (he wrote numerous), preludes, some of his mazurkas, one of the three sonatinas would be good performance material.
Any of the etudes by Grazyna Bacewicz are pretty bad-ass stage pieces.
If you can step it up a few minutes, you could bust out Edison Denisov's Variations, which is a really interesting atonal work with lots of rhythmic fun.
Maybe also look into American composer Allan Brings, who has many works available for free perusal at
https://www.amc.net/composers/c_works.asp?ComposerID=17699&ActorID=33017 . I've little knowledge of his piano works but his composing style is solidly modern and he's contributed lots to American keyboard literature.
Aside from that, why not dig through the recent literature by Walter Hus (any of his prelude and fugue pairs are pretty stunning), Lera Auerbach (tons of works), Rzewski (tons and tons of works, maybe do a few "miles" from 'The Road'), John White (writer of 100+ short sonatas).
I would suggest all of these folks over a composer like Sorabji, though I do like his work also. The Ligeti piece you mentioned is cool as hell, but I feel like it's becoming one of those "required greatest hit" pieces that a lot of players choose more because of its notoriety and wow-factor and less because of its actual musical content. Don't get me wrong, I'm not labelling you with this criticism. I just feel like every modern-music-loving pianist I've met under 25 seems to feel like they
have to do that piece and I'm like "man....why not one of the other studies?...it's not like they're
not awesome or anything." That being said, I'm sure plenty of you have seen that corny video that some high school pianist made of him performing the Devil's Staircase. The performance was good, but his introduction to the performance was just plain goofy. He said something like "welcome to hell!" or some otherwise ludicrous bollocks.
Topic: Modern piece suggestions