This design will control 64 LEDs. You need 72. So what you can is add additional banks of LEDs, and control additional transisitors with a shift register instead. Or a shift register with high current sinking capability, such as TPIC6B595, and skip the transistors.
Take it a step further, and drive the anodes from 2 shift registers, and free up IO pins for buttons for setting time, retrieving time from an Real Time Clock chip, etc.
