[Nexus]

Набросал на коленке, есть что улучшить.

/**
 * @param {Date} start
 * @param {Date} finish
 * @param {int} activityDurationInSeconds
 * @param {int} [breakInSeconds]
 * @return {array}
 */
function makeSchedule(start, finish, activityDurationInSeconds, breakInSeconds = 0) {
    [start, finish] = [start, finish].map(val => +val).sort((a, b) => a - b);
    
    const formatter = dateTime => {
        return [
            dateTime.getHours(),
            dateTime.getMinutes(),
        ].map(val => val > 9 ? val : '0' + val).join(':');
    }
    
    const result = [];
    const setDate = (date => milliseconds => {
        date.setTime(milliseconds);
        
        return date;
    })(new Date());
    
    let time = start;
    while (time < finish) {
        result.push([
            formatter( setDate(time) ),
            formatter( setDate(time += activityDurationInSeconds * 1000) )
        ]);
        
        time += breakInSeconds * 1000;
    }
    
    return result;
}

console.table(
    makeSchedule(
        new Date().setHours(08, 00), 
        new Date().setHours(16, 00), 
        15 * 60, // convert minutes to seconds
        0
    )
);