How can I show a toast for a specific duration?

I found this answer. Albeit a bit more complex it also allows you to create toasts longer than Toast.LENGTH_LONG. You might have to change the tick duration from 1000ms to 500ms.

private Toast mToastToShow;
public void showToast(View view) {
   // Set the toast and duration
   int toastDurationInMilliSeconds = 10000;
   mToastToShow = Toast.makeText(this, "Hello world, I am a toast.", Toast.LENGTH_LONG);

   // Set the countdown to display the toast
   CountDownTimer toastCountDown;
   toastCountDown = new CountDownTimer(toastDurationInMilliSeconds, 1000 /*Tick duration*/) {
      public void onTick(long millisUntilFinished) {
         mToastToShow.show();
      }
      public void onFinish() {
         mToastToShow.cancel();
         }
   };

   // Show the toast and starts the countdown
   mToastToShow.show();
   toastCountDown.start();
}

Here is how it works: the countdown has a notification time shorter than the duration for which the toast is displayed according to the flag, so the toast can be shown again if the countdown is not finished. If the toast is shown again while it is still on screen, it will stay there for the whole duration without blinking. When the countdown is finished, the toast is cancelled to hide it even if its display duration is not over.

This works even if the toast must be shown for a duration shorter than the default duration: the first toast displayed will simply be cancelled when the countdown is finished.

Adding to @Senth's answer, if you don't wont to accumulate the time when you call the showToast method multiple times, with the same Message:

private Toast mToastToShow = null;
String messageBeingDisplayed = "";

/**
 * Show Toast message for a specific duration, does not show again if the message is same
 *
 * @param message     The Message to display in toast
 * @param timeInMSecs Time in ms to show the toast
 */
public void showToast(String message, int timeInMSecs) {
    if (mToastToShow != null && message.equals(messageBeingDisplayed)) {
        Log.d("DEBUG", "Not Showing another Toast, Already Displaying");
        return;
    } else {
        Log.d("DEBUG", "Displaying Toast");
    }
    messageBeingDisplayed = message;
    // Set the toast and duration
    int toastDurationInMilliSeconds = timeInMSecs;
    mToastToShow = Toast.makeText(this, message, Toast.LENGTH_LONG);

    // Set the countdown to display the toast
    CountDownTimer toastCountDown;
    toastCountDown = new CountDownTimer(toastDurationInMilliSeconds, timeInMSecs /*Tick duration*/) {
        public void onTick(long millisUntilFinished) {
            if (mToastToShow != null) {
                mToastToShow.show();
            }
        }

        public void onFinish() {
            if (mToastToShow != null) {
                mToastToShow.cancel();
            }
            // Making the Toast null again
            mToastToShow = null;
            // Emptying the message to compare if its the same message being displayed or not
            messageBeingDisplayed = "";
        }
    };

    // Show the toast and starts the countdown
    mToastToShow.show();
    toastCountDown.start();
}

You can display toast now for 500 ms like this:

showToast("Not Allowed", 500);

This cannot be done. To show a toast for a length shorter than Toast.LENGTH_SHORT, you must cancel it after the time you want. Something like:

final Toast toast = Toast.makeText(getApplicationContext(), "This message will disappear in half a second", Toast.LENGTH_SHORT);
    toast.show();

    Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
           @Override
           public void run() {
               toast.cancel(); 
           }
    }, 500);