function exam([arg1, arg2, arg3, arg4]) {

    let examHour = Number(arg1);
    let exanMin = Number(arg2);
    let arriveHour = Number(arg3);
    let arriveMin = Number(arg4);

    let examTime = examHour * 60 + exanMin;
    let arriveTime = arriveHour * 60 + arriveMin;

    let totalMinutesDifference = arriveTime - examTime;
    let secondDiff = examTime - arriveTime;

    if (totalMinutesDifference <= 59 && totalMinutesDifference > 0) {
        console.log('Early');
    } else if (totalMinutesDifference >= 30) {
        console.log('On time');
    }

    if (totalMinutesDifference != 0) {
        let hoursDifference = Math.abs(totalMinutesDifference / 60);
        let minutesDifference = Math.abs(totalMinutesDifference % 60);

        if (minutesDifference > 0) {
            console.log(minutesDifference + ' minutes before the start');
        } else if (hoursDifference) {
            console.log(`${hoursDifference}:${minutesDifference}` + ' hours before the start');

        }
        if (totalMinutesDifference < 0) {
            console.log(`${minutesDifference}` + ' minutes after the start');
        } else {
            console.log(`${hoursDifference}:${minutesDifference}` + ' hours after the start');
    }

}

exam(['9', '30', '9', '50']);