Sorry for my bad english! I hope you are getting it: I am using datepicker and timepicker as standalone instances on one single page. By using the "altField" the base "_updateAlternate" sets the val() of the altField to the date value of the datepickers, not to the properly val() of the timepickers instances. So i override it and check if the "altFieldTimeOnly" option is set and then put the right formatted time in the altField's val().

Author: marvinschroeder

jquery-ui-timepicker-addon.js

@@ -1158,6 +1158,28 @@ $.datepicker._setDateDatepicker = function(target, date) {
 	this._setTimeDatepicker(target, tp_date, true);
 };
 
+//#######################################################################################
+//override _updateAlternate() to avoid date strings on altFields at initalization if
+//using datepicker and timepicker as standalone on one page
+//#######################################################################################
+$.datepicker._updateAlternate = function(inst) {
+    var altField = this._get(inst, 'altField');
+    if (altField) { // update alternate field too
+        var altFormat = this._get(inst, 'altFormat') || this._get(inst, 'dateFormat');
+        var date = this._getDate(inst);
+        var timeOnly = this._get(inst, 'altFieldTimeOnly');
+        if(timeOnly){
+            tp_inst = this._get(inst, 'timepicker');            
+            tp_inst._formatTime();
+            var dateStr = tp_inst.formattedTime;
+            $(altField).each(function() { $(this).val(dateStr); });
+        } else {
+            var dateStr = this.formatDate(altFormat, date, this._getFormatConfig(inst));
+            $(altField).each(function() { $(this).val(dateStr); });
+        }
+    }
+}
+
 //#######################################################################################
 // override getDate() to allow getting time too within Date object
 //#######################################################################################