The 30 minute setlist presents an interesting challenge. It's tempting to use Mirror of Souls and a couple of others, but a show like that your audience likely has many who aren't familiar with the band. So I think something that gives a broader spectrum is necessary - gives the uninitiated a better feel for their music.
I'm thinking this.
1. Altar to the Unknown God
2. Wages of Sin
3. Mountain
4. I AM
5. Absolution Day
31 minutes 44 seconds - close enough, right? Of course you do need one big epic, since that's one of the things Theocracy is known for. Since MOS is off the table, I'm going with I AM. Twist of Fate would be another excellent choice, but I'm guessing I AM would have a broader appeal.
If they were to do a short set that includes MOS, I think the following would work well.
1. 30 Pieces of Silver
2. Mountain
3. Mirror of Souls