Inspired by #Linear RGB LED Clockby Jan I decided to build my version. Instead of RGB LED addressable strip I'll be using regular LEDs and shift registers.

As I am planning to use the cheap chinese Digispark boards and a minimal of components. Since RESET pin is not available as I/O in most of the cheap boards I have only 5 pins to spare.

Two pins are for I2C communication with the RTC module

One pin will drive the shift registers using Roman Black's 1 bit shift system

The last two pins will be shared by a button and an LED each. Thus I need only three 8 bit shift registers (74HC595) for driving the remaining 24 LEDs

here's the draft for the circuit.