Interrupt based Clock for ATMega328p & KEL Shield

#include "lib.h" // lib.h from http://pastebin.com/Bzz5PRcx

unsigned long timeInMinutes = 0;
unsigned long long minutesCounter = 0;
unsigned int dotCounter = 0;

unsigned char cursor = 0; // 0 - sati, 1 - minuti

unsigned char display[5] = {SEG7_1, SEG7_1, SEG7_1, SEG7_1};



void makeClock(unsigned char *display_buffer, int num) {
    unsigned char numbers[] = { SEG7_0, SEG7_1, SEG7_2, SEG7_3, SEG7_4, SEG7_5,
    SEG7_6, SEG7_7, SEG7_8, SEG7_9 };

    unsigned int minutes = num % 60;
    unsigned int hours = (num / 60) % 24;

    display_buffer[3] = numbers[minutes % 10];
    display_buffer[2] = numbers[minutes / 10];

    display_buffer[1] = numbers[hours % 10];
    display_buffer[0] = numbers[hours / 10];


    if (display_buffer[0] == SEG7_0) {
        display_buffer[0] = SEG7_NULL;
    }
}

ISR(TIMER0_COMPA_vect) {
    minutesCounter++;
    dotCounter++;

    if (minutesCounter == 60000) {
        timeInMinutes++;
        makeClock(display, timeInMinutes);
        minutesCounter = 0;
    }
    if (dotCounter == 500) {
        display[1] &= 0b11111011;
    } else if (dotCounter == 1000) {
        display[1] |= 0b00000100;
        dotCounter = 0;
    }
}

ISR(PCINT1_vect) {
    // Interrupt
}

int main() {
    init7seg();
    initTimer();
    initButtons();

    makeClock(display, 0);

    while (1) {
        if (readButton('l') == 1) {
            cursor = 0;
        }
        if (readButton('r') == 1) {
            cursor = 1;
        }

        if (readButton('u') == 1) {
            if (cursor == 1) {
                timeInMinutes += 1;
            } else {
                timeInMinutes += 60;
            }
            makeClock(display, timeInMinutes);
            while (readButton('u') == 1) print7segWord(display);
        }

        if (readButton('d') == 1) {
            if (cursor == 1) {
                timeInMinutes -= 1;
            } else {
                timeInMinutes -= 60;
            }
            makeClock(display, timeInMinutes);
            while (readButton('d') == 1) print7segWord(display);
        }

        print7segWord(display);
    }
}