gistfile1.sql

;WITH base AS
     ( 
     SELECT  UserId,
			DateUtc,
             ROW_NUMBER() over (partition BY UserId ORDER BY DateUtc) AS rn
     FROM     dbo.UserActivity WHERE DateUtc Between @startDate and @endDate
     )

SELECT b1.UserId,
	SUM(CASE 
	WHEN 
		DATEDIFF(year,b1.DateUtc,b2.DateUtc) = 0 AND DATEDIFF(day,b1.DateUtc, b2.DateUtc) = 0 AND DATEDIFF(mi, b1.DateUtc, b2.DateUtc) >= @minsForUnique THEN 1 
	WHEN
		DATEDIFF(year,b1.DateUtc,b2.DateUtc) = 0 AND DATEDIFF(day,b1.DateUtc, b2.DateUtc) != 0 THEN 1
	ELSE 0 END) as [TotalUnique]
FROM base b1
INNER JOIN base b2 ON b1.UserId = b2.UserId AND b1.rn != b2.rn
GROUP BY b1.UserId