SQL:vind continue datumbereiken over meerdere rijen?

Voorbeeldgegevens

create table tbl (person int, startdate datetime, enddate datetime, hours decimal(10,2));
insert tbl values
(5163 ,'2013-04-29 07:00:00.000' ,'2013-04-29 11:00:00.000', 4.00),
(5163 ,'2013-04-29 11:30:00.000' ,'2013-04-29 15:30:00.000', 4.00),
(5163 ,'2013-04-29 15:30:00.000' ,'2013-04-29 19:06:00.000', 3.60),
(5851 ,'2013-05-02 19:00:00.000' ,'2013-05-02 23:00:00.000', 4.00),
(5851 ,'2013-05-02 23:00:00.000' ,'2013-05-03 00:00:00.000', 1.00),
(5851 ,'2013-05-03 00:00:00.000' ,'2013-05-03 00:31:00.000', 0.52);

De vraag

;with cte as (
    select person, startdate, enddate, hours
    from tbl
    union all
    select t.person, cte.startdate, t.enddate, cast(cte.hours + t.hours as decimal(10,2))
    from cte
    join tbl t on cte.person = t.person and cte.enddate = t.startdate
), cte2 as (
    select *, rn = row_number() over (partition by person, enddate order by startdate)
    from cte
)
select person, startdate, max(enddate) enddate, max(hours) hours
from cte2
where rn=1
group by person, startdate
order by person, startdate;

Resultaten

person      startdate               enddate                 hours
----------- ----------------------- ----------------------- -------
5163        2013-04-29 07:00:00.000 2013-04-29 11:00:00.000 4.00
5163        2013-04-29 11:30:00.000 2013-04-29 19:06:00.000 7.60
5851        2013-05-02 19:00:00.000 2013-05-03 00:31:00.000 5.52