After fixing some minor bugs in the schematics and optimizing the current consumption (the LED's are better than their spec), I tried out the upper section of the clock. The bottom is just a mirrored version except the reset logic @24:00, but this shouldn't be any problem.

What you see in the video: 

The 8 top PCBs are the FF's that for two Johnson counters. The 3 on the right will be used for the tens (minutes) and the others for the ones (hours). The Decoder on the right generates the "carry over" clock pulse for the left block. The yellow LEDs are for testing the decoder. Both work but I was too lazy to make two blocks for the video...

Now I need to order more female pin headers for the lower part, since I totally miscalculated the amount I needed... I still have to wait for the Digit PCBs anyway. Stay tuned!