Do try
Bartók's Bluebeard's Castle (1911), which is only an hour, or Richard
Strauss' Salome, which is about 90 minutes, although from 1905, it doesn't quite make your time cut!
The two-character Bartók is my favorite opera, and the Strauss is not far behind. The latter has one of the most blazing, difficult final scenes of anything, anywhere, and is often lifted out as a concert showpiece for soprano and orchestra.
The three other choices you mention are excellent: imaginative, and from composers quite different from each other, so they would give you a very good survey. I would also explore at least one opera by
Janáček, such as
Káťa Kabanová (1921) or
The Cunning Little Vixen (1924) -- any of them, really! -- just to see if you like his language. Same thing for virtually any of
Britten's operas. My favorite is probably
Peter Grimes (1945) but again, many of them are marvelous.
For things written more recently, you might try
Ligeti's Le Grande Macabre (1975-77, revised version 1996), just because it's so wild, and again, who knows? You might totally love it.

--Bruce