public String getHoursString() {
            return timeUnits == HH_MM_SS || timeUnits == HH_MM ? input.substring(0, 2) : "00";
        }
Encapsulates the digit input logic and text to duration conversion logic.
android/third_party/time-duration-picker/src/main/java/mobi/upod/timedurationpicker/TimeDurationPicker.java