unnamed.java

public long getTime(){
    long time = getServer().getWorld("world").getTime();
    return time;
}

// somewhere
    bool justMidnight = false;

...
    getServer().getScheduler().scheduleSyncRepeatingTask(this, new Runnable() {
        @Override
        public void run() {
            if (getTime() >= 0 && getTime() <= 0100) {
                if (!justMidnight) {
                    justMidnight = true;
                    // do something
                }
            } else {
                justMidnight = false;
            }
        }
    }, 0, 100);