-- Ваши исходные данные:
with
  [time] (id, [date], time_from) as
    (
      select i, cast(d as date) as d, cast(t as datetime) as t
        from (values
                (461310,'2019-02-10','2019-02-10 12:00:00'),
                (461310,'2019-02-11','2019-02-11 10:00:00'),
                (461310,'2019-02-11','2019-02-11 11:00:00'),
                (461310,'2019-02-11','2019-02-11 12:00:00'),
                (461310,'2019-02-11','2019-02-11 15:00:00'),
                (461310,'2019-02-11','2019-02-11 16:00:00'),
                (461310,'2019-02-11','2019-02-11 18:00:00'),
                (461310,'2019-02-11','2019-02-11 19:00:00'),
                (461310,'2019-02-11','2019-02-11 20:00:00')
             ) v(i,d,t)
    )
--
-- Один из возможных вариантов запроса:
select id as technician_id
     , [date]
     , time_from
     , cast(time_from as time) as [hour]
     , row_number() over(partition by id, date, grp_id order by time_from desc) as megarank
  from (
         select s.*
             -- Ключевой момент запроса:
              , datepart(hour, time_from) - row_number()over(partition by id, date order by time_from) as grp_id 
           from [time] as s
       ) as v
 order by id, time_from