So, what is the difference this time? I have used TM1637 four-digit, seven-segment display, instead of driverlesss display. The difference is in the number of components. Instead of having twelve resistors and four transistors to drive the 7-segment display, now I have a single display with the built-in driver.

The code is on github.
Here is the schematics:

When you compare that to my previous 4-digit 7-segment build, you will notice the difference. The code is simpler, too:

const int CLK = 17; //Set the CLK pin connection to the display
const int DIO = 16; //Set the DIO pin connection to the display
TM1637Display display(CLK, DIO); //set up the 4-Digit Display.
void setup() {
//set the display brightness (0x0a is max)
display.setBrightness(0x05);
...
}
void loop() {
display.showNumberDec(hour_1*1000 + hour_2*100 + minute_1*10 + minute_2);
toggle = ~toggle;
if (toggle)
{
display.showNumberDecEx(hour_1*1000 + hour_2*100 + minute_1*10 + minute_2, (0x80 >> 1), true);
}
delay(500);
}

This is the clock: