chris83:
ATTiny85 - cheaper and seems to have enough pins available for this[/li][/list]Will this work? Do you see any issues with the circuit? Can it be simplified further?
Hi Chris,
Your design has lots of opportunities to learn about shift registers, driver transistors, ICSP programming etc, which is great. But it could be simpler and cheaper! Using an ATtiny85 might seem like a cheap option, but when you add in the cost of the other ICs, you probably could have used at ATmega328, which would have enough pins to do what you want with perhaps only those BC558's to help it. Another simpler option would be max7219 as Paul__B says.
Next problem: accuracy of your clock. Relying on the ATtiny's internal oscillator, its not going to be very good! Also, each time you disconnect power/change batteries, the time will have to be re-set. You could use an RTC, such as DS1307 or better still DS3231.
Paul