The source code

    /*!
     * Ext JS Library 3.4.0
     * Copyright(c) 2006-2011 Sencha Inc.
     * licensing@sencha.com
     * http://www.sencha.com/license
     */
    /**
     * @class Ext.form.TimeField
     * @extends Ext.form.ComboBox
     * Provides a time input field with a time dropdown and automatic time validation.  Example usage:
     *
    new Ext.form.TimeField({
        minValue: '9:00 AM',
        maxValue: '6:00 PM',
        increment: 30
    });

     * @constructor
     * Create a new TimeField
     * @param {Object} config
     * @xtype timefield
     */
    Ext.form.TimeField = Ext.extend(Ext.form.ComboBox, {
        /**
         * @cfg {Date/String} minValue
         * The minimum allowed time. Can be either a Javascript date object with a valid time value or a string
         * time in a valid format -- see {@link #format} and {@link #altFormats} (defaults to undefined).
         */
        minValue : undefined,
        /**
         * @cfg {Date/String} maxValue
         * The maximum allowed time. Can be either a Javascript date object with a valid time value or a string
         * time in a valid format -- see {@link #format} and {@link #altFormats} (defaults to undefined).
         */
        maxValue : undefined,
        /**
         * @cfg {String} minText
         * The error text to display when the date in the cell is before minValue (defaults to
         * 'The time in this field must be equal to or after {0}').
         */
        minText : "The time in this field must be equal to or after {0}",
        /**
         * @cfg {String} maxText
         * The error text to display when the time is after maxValue (defaults to
         * 'The time in this field must be equal to or before {0}').
         */
        maxText : "The time in this field must be equal to or before {0}",
        /**
         * @cfg {String} invalidText
         * The error text to display when the time in the field is invalid (defaults to
         * '{value} is not a valid time').
         */
        invalidText : "{0} is not a valid time",
        /**
         * @cfg {String} format
         * The default time format string which can be overriden for localization support.  The format must be
         * valid according to {@link Date#parseDate} (defaults to 'g:i A', e.g., '3:15 PM').  For 24-hour time
         * format try 'H:i' instead.
         */
        format : "g:i A",
        /**
         * @cfg {String} altFormats
         * Multiple date formats separated by "|" to try when parsing a user input value and it doesn't match the defined
         * format (defaults to 'g:ia|g:iA|g:i a|g:i A|h:i|g:i|H:i|ga|ha|gA|h a|g a|g A|gi|hi|gia|hia|g|H|gi a|hi a|giA|hiA|gi A|hi A').
         */
        altFormats : "g:ia|g:iA|g:i a|g:i A|h:i|g:i|H:i|ga|ha|gA|h a|g a|g A|gi|hi|gia|hia|g|H|gi a|hi a|giA|hiA|gi A|hi A",
        /**
         * @cfg {Number} increment
         * The number of minutes between each time value in the list (defaults to 15).
         */
        increment: 15,

        // private override
        mode: 'local',
        // private override
        triggerAction: 'all',
        // private override
        typeAhead: false,

        // private - This is the date to use when generating time values in the absence of either minValue
        // or maxValue.  Using the current date causes DST issues on DST boundary dates, so this is an
        // arbitrary "safe" date that can be any date aside from DST boundary dates.
        initDate: '1/1/2008',

        initDateFormat: 'j/n/Y',

        // private
        initComponent : function(){
            if(Ext.isDefined(this.minValue)){
                this.setMinValue(this.minValue, true);
            }
            if(Ext.isDefined(this.maxValue)){
                this.setMaxValue(this.maxValue, true);
            }
            if(!this.store){
                this.generateStore(true);
            }
            Ext.form.TimeField.superclass.initComponent.call(this);
        },

        /**
         * Replaces any existing {@link #minValue} with the new time and refreshes the store.
         * @param {Date/String} value The minimum time that can be selected
         */
        setMinValue: function(value, /* private */ initial){
            this.setLimit(value, true, initial);
            return this;
        },

        /**
         * Replaces any existing {@link #maxValue} with the new time and refreshes the store.
         * @param {Date/String} value The maximum time that can be selected
         */
        setMaxValue: function(value, /* private */ initial){
            this.setLimit(value, false, initial);
            return this;
        },

        // private
        generateStore: function(initial){
            var min = this.minValue || new Date(this.initDate).clearTime(),
                max = this.maxValue || new Date(this.initDate).clearTime().add('mi', (24 * 60) - 1),
                times = [];

            while(min <= max){
                times.push(min.dateFormat(this.format));
                min = min.add('mi', this.increment);
            }
            this.bindStore(times, initial);
        },

        // private
        setLimit: function(value, isMin, initial){
            var d;
            if(Ext.isString(value)){
                d = this.parseDate(value);
            }else if(Ext.isDate(value)){
                d = value;
            }
            if(d){
                var val = new Date(this.initDate).clearTime();
                val.setHours(d.getHours(), d.getMinutes(), d.getSeconds(), d.getMilliseconds());
                this[isMin ? 'minValue' : 'maxValue'] = val;
                if(!initial){
                    this.generateStore();
                }
            }
        },

        // inherited docs
        getValue : function(){
            var v = Ext.form.TimeField.superclass.getValue.call(this);
            return this.formatDate(this.parseDate(v)) || '';
        },

        // inherited docs
        setValue : function(value){
            return Ext.form.TimeField.superclass.setValue.call(this, this.formatDate(this.parseDate(value)));
        },

        // private overrides
        validateValue : Ext.form.DateField.prototype.validateValue,

        formatDate : Ext.form.DateField.prototype.formatDate,

        parseDate: function(value) {
            if (!value || Ext.isDate(value)) {
                return value;
            }

            var id = this.initDate + ' ',
                idf = this.initDateFormat + ' ',
                v = Date.parseDate(id + value, idf + this.format), // *** handle DST. note: this.format is a TIME-only format
                af = this.altFormats;

            if (!v && af) {
                if (!this.altFormatsArray) {
                    this.altFormatsArray = af.split("|");
                }
                for (var i = 0, afa = this.altFormatsArray, len = afa.length; i < len && !v; i++) {
                    v = Date.parseDate(id + value, idf + afa[i]);
                }
            }

            return v;
        }
    });
    Ext.reg('timefield', Ext.form.TimeField);