[Advice needed] Building a small BCD clock.

Other Hardware LEDs and Multiplexing
8

As you are building a BCD clock I would use an ATTiny with at least 8 outputs and arrange your leds on a 4x4 grid (with gaps where you dont need LEDs)

Then you can use 4 of your outputs for your rows and four for you columns and you have an easier solution than charlieplexing. You would need to row scan the rows of the 4x4 matrix but there are loads of tutorials on how to do that on these forums and on the net.

Something like
X X
X X X
X X X X
X X X X
Hours Minutes

HTH