This code passes all test cases

public static long minimumAverage(List> customers) { // Write your code here // Assumption from the problem statement: // 1. The first order is always cooked first.

    customers.sort(new Comparator<List<Integer>>() {
        public int compare(List<Integer> o1, List<Integer> o2)
        {
            return o1.get(0) - o2.get(0);
        }
    });
    PriorityQueue<List<Integer>> cookQueue = new PriorityQueue<>();
    PriorityQueue<List<Integer>> orderQueue = new PriorityQueue<>(new Comparator<List<Integer>>()
    {
        public int compare(List<Integer> o1, List<Integer> o2)
        {
            return o1.get(1) - o2.get(1); // Sort based on cook time.
        }
    }); 
    long totalCookTime = 0;
    long totalWaitTime = 0;

    if(customers.isEmpty())
        return 0;
    // The first order is always cooked first
    cookQueue.add(customers.get(0));
    for(int i = 1; i < customers.size(); i++)
        orderQueue.add(customers.get(i));
    long firstOrderTime = cookQueue.peek().get(0);
    while(!cookQueue.isEmpty())
    {
        List<Integer> order = cookQueue.remove();
        int orderTime = order.get(0);
        int cookTime = order.get(1);
        totalCookTime += cookTime;
        totalWaitTime += (totalCookTime + firstOrderTime - orderTime);

        List<List<Integer>> holding = new ArrayList<>();
        while(!orderQueue.isEmpty() && orderQueue.peek().get(0) > (totalCookTime + firstOrderTime))
            holding.add(orderQueue.remove());
        if(!orderQueue.isEmpty())
            cookQueue.add(orderQueue.remove()); 
        if(!holding.isEmpty())
            orderQueue.addAll(holding); 

        // If there is a gap between order time and cook time (pizza oven idles)
        if(cookQueue.isEmpty() && !orderQueue.isEmpty())
        {
            cookQueue.add(orderQueue.remove());
            firstOrderTime = cookQueue.peek().get(0); //Reset the anchor point. 
            totalWaitTime = 0;
        }
    } 
    return totalWaitTime / customers.size();
}