SELECT
	a.PackUser,
	a.OrderId,
	a.PackDate,
	b.OrderId AS AdjacentOrderId,
	b.PackDate AS AdjacentPackDate
FROM
	YourTable a
	CROSS APPLY
	(
		SELECT TOP 1 b.OrderId, b.PackDate
		FROM YourTable b
		WHERE b.PackUser = a.PackUser
			AND DATEDIFF(second,a.PackDate,b.PackDate) < 60
	) b;

CREATE TABLE #Packs
(Packuser INT, OrderId INT, PackDate DATETIME);
INSERT INTO #packs VALUES
(1,100, '2012-07-13 14:26:37.380'),
(1,101, '2012-07-13 14:26:39.380'),
(1,102, '2012-07-13 14:27:39.000'),
(1,103, '2012-07-12 14:27:39.000'),
(2,104, '2012-07-12 14:27:39.000'),
(2,105, '2012-07-13 14:27:39.000'),
(3,106, '2012-07-13 14:27:39.000'),
(4,107, '2012-07-13 14:27:39.000'),
(5,108, '2012-07-13 14:27:39.000'),
(5,109, '2012-07-13 14:26:40.000')

SELECT
	a.PackUser,
	a.OrderId,
	a.PackDate,
	b.OrderId AS AdjacentOrderId,
	b.PackDate AS AdjacentPackDate
FROM
	#packs a
	CROSS APPLY
	(
		SELECT TOP 1 b.OrderId, b.PackDate
		FROM #packs b
		WHERE b.PackUser = a.PackUser
			AND DATEDIFF(second,a.PackDate,b.PackDate) BETWEEN 0 AND 60
			AND a.orderId <> b.OrderId
			AND DATEADD(dd,DATEDIFF(dd,0,b.PackDate),0) = DATEADD(dd,DATEDIFF(dd,0,GETDATE()),0)
		ORDER BY b.PackDate ASC
	) b;
	
DROP TABLE #packs;