Sample code for count down timer.

CountDownTimer.java

    String FORMAT = "dd/MM/yyyy";
    private CountDownTimer mTimer;

    public void startTimer() {
        SimpleDateFormat sdfNew = new SimpleDateFormat(FORMAT);
        String date = sdfNew.format(new Date());
        String endingDate = "";
        if (isBefore(date, "12/10/2018")) {
            endingDate = "12/10/2018";
        } else if (isBefore(date, "14/10/2018")) {
            endingDate = "14/10/2018";
        }

        mTimer = new CountDownTimer(getEndingMiliseconds(endingDate), 1000) {
            public void onTick(long millisUntilFinished) {
                int seconds = (int) (millisUntilFinished / 1000);
                int hours = seconds / 3600;
                int minutes = (seconds % 3600) / 60;
                seconds = seconds % 60;

                String hourss = String.format("%02d", hours);
                String minutess = String.format("%02d", minutes);
                String secondss = String.format("%02d", seconds);
                Log.e("TIMER", "onTick: " + hourss + ":" + minutess + ":" + secondss);
            }

            public void onFinish() {
                Log.e("TIMER", "Timer finished: ");
            }
        }.start();
    }

    public long getEndingMiliseconds(String endingTime) {
        try {
            DateFormat df = new SimpleDateFormat(FORMAT);
            Date date1 = new Date();
            Date date2 = df.parse(endingTime);
            long diff = date2.getTime() - date1.getTime();
            return diff;
        } catch (ParseException e) {
            Log.e("TEST", "Exception", e);
        }
        return 0;
    }

    public boolean isBefore(String startDate, String endDate) {
        try {
            SimpleDateFormat df = new SimpleDateFormat(FORMAT);
            Date dateStart = df.parse(startDate);
            Date dateEnd = df.parse(endDate);

            return dateStart.before(dateEnd);
        } catch (Exception e) {
            return false;
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        if (mTimer != null) {
            mTimer.cancel();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        startTimer();
    }