The source code

    /**
     * @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 null).
         */
        minValue : null,
        /**
         * @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 null).
         */
        maxValue : null,
        /**
         * @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').
         */
        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",
        /**
         * @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',

        // private
        initComponent : function(){
            if(typeof this.minValue == "string"){
                this.minValue = this.parseDate(this.minValue);
            }
            if(typeof this.maxValue == "string"){
                this.maxValue = this.parseDate(this.maxValue);
            }

            if(!this.store){
                var min = this.parseDate(this.minValue) || new Date(this.initDate).clearTime();
                var max = this.parseDate(this.maxValue) || new Date(this.initDate).clearTime().add('mi', (24 * 60) - 1);
                var times = [];
                while(min <= max){
                    times.push(min.dateFormat(this.format));
                    min = min.add('mi', this.increment);
                }
                this.store = times;
            }
            Ext.form.TimeField.superclass.initComponent.call(this);
        },

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

        // private
        beforeBlur : function(){
            var v = this.parseDate(this.getRawValue());
            if(v){
                this.setValue(v.dateFormat(this.format));
            }
            Ext.form.TimeField.superclass.beforeBlur.call(this);
        }

        /**
         * @cfg {Boolean} grow @hide
         */
        /**
         * @cfg {Number} growMin @hide
         */
        /**
         * @cfg {Number} growMax @hide
         */
        /**
         * @hide
         * @method autoSize
         */
    });
    Ext.reg('timefield', Ext.form.TimeField);