What do you do with 144 7-segment ... the clock with a single Arduino Nano. Even charlieplexing won’t get you that many I/O lines. The solution was a nifty little chip called the MAX7219.

[David Hopkins] built a seven segment clock ... The easy part consists of Neopixels, an Arduino Nano and a DS3231 Real Time Clock. The hard part consists of Plasticard and a polymorph diffuser.