Sort Flex 3 ArrayCollection by datetime value

How do you sort datetimes in a flex3 data object? I have an ArrayCollection with many arrays that look like this: {time:2008-08-06 01:00:00-07, KwH:30000} and I need to sort the arraycollection on the time field in each array.

Here is all the code that is generating this problem for me

private function generate_time_series_average():void
			{
				var all_devices:ArrayCollection = new ArrayCollection();
				for each(var ds:Object in data_services)
				{
					var the_ds:XML = new XML(ds.data_service.lastResult);
					for each(var reading:XML in the_ds.children())
					{
						all_devices.addItem({time:reading.time, KwH:reading.KwH});
					}
				}
				
				// Sort by datetime then by did
				var timeSortField:SortField = new SortField();
				timeSortField.name = "time";
				timeSortField.compareFunction = date_sort_function;
				
				var all_devices_sort:Sort = new Sort();
				all_devices_sort.fields = [timeSortField];
				
				all_devices.sort = all_devices_sort;
				all_devices.refresh();
				
				// Loop through sorted data to generate averages..add to time_series_average
				var count:int = 0;
				var total:int = 0;
				for(var i:int = 0; i < all_devices.length; i++)
				{
					if(count == data_services.length)
						count = 0;
					else
						count = count + 1;
					var this_item:Object = all_devices.getItemAt(i);
					total = total + parseInt(this_item.KwH);
					if(count == data_services.length)
					{
						var beforeCalc:int = total;
						total = (total / count);
						Alert.show("Adding this total for " + this_item.time + ": " + total + "\nIt was calculated like this: (" + beforeCalc + "/" + count + ")");
						time_series_average.addItem({time:this_item.time, KwH:total});
						count = 0;
						total = 0;
					}
				}
			}
			
			private function date_sort_function(a:Object, b:Object):int
			{
				/*
				var tempDateA:Date = new Date(Date.parse(this.fix_a_date(a.toString())));
				var tempDateB:Date = new Date(Date.parse(this.fix_a_date(b.toString())));
			
				return ObjectUtil.dateCompare(tempDateA, tempDateB);
				*/
				var d1ms:Number = new Date(a.time).getTime();
				var d2ms:Number = new Date(a.time).getTime();
				
				if(d1ms > d2ms)
				{
					return -1;
				}
				else if(d1ms < d2ms)
				{
					return 1;
				}
				else
				{
					return 0;
				}
			}

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