code: public static <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) throws RejectedExecutionException, CouldNotPerformException {
          if (callable == null) {
              throw new NotAvailableException("callable");
          }
          return getInstance().executorService.schedule(callable, delay, unit);
      }
docs: @see java.util.concurrent.ScheduledExecutorService
  
  @param callable the function to execute
  @param delay the time from now to delay execution
  @param unit the time unit of the delay parameter
  @param <V> the type of the callable's result
  @return a ScheduledFuture that can be used to extract result or cancel
  @throws RejectedExecutionException if the task cannot be scheduled for execution
  @throws NotAvailableException if callable is null