declare @TimeRanges as TABLE (SessionStart datetime, SessionEnd datetime);

     with TimeRanges as (
  select @Start as StartTime, @Start + @TimeRange as EndTime
  union all
  select StartTime + @TimeRange, EndTime + @TimeRange
    from TimeRanges
    where EndTime  < @Finish )

;with cte as
(
    select SessionStartTime as changetime,1 as CC from Calls
    union all
    select SessionCloseTime,-1 from Calls
)
    select top 1 changetime,rt from
    (
    select * from cte
        cross apply
        (select SUM(cc) as rt from cte c where c.changetime<=cte.changetime) rt
    ) v
    order by rt desc

@Start datetime,
    @Finish datetime,
    @TimeRange time
AS
BEGIN

    SET NOCOUNT ON;
    declare @res int SET @res = 0

    declare @TimeRanges as TABLE (SessionStart datetime, SessionEnd datetime);

    with TimeRanges as
     (  select @Start as StartTime, @Start + @TimeRange as EndTime
        union all
        select StartTime + @TimeRange, EndTime + @TimeRange
        from TimeRanges
        where EndTime  < @Finish ),


    cte as
    (
    select SessionStart as changetime,1 as CC from TimeRanges
    union all
    select SessionEnd,-1 from TimeRanges
    )
    select top 1 changetime,rt from
    (
    select * from cte
        cross apply
        (select SUM(cc) as rt from cte c where c.changetime<=cte.changetime) rt
    ) v
    order by rt desc


    select StartTime, EndTime,cte.rt
    from TimeRanges as TR left outer join
      dbo.Test as Test on TR.StartTime <= Test.SessionStartTime
      and Test.SessionCloseTime < TR.EndTime
    where Test.ScenarioID = 24
    group by TR.StartTime, TR.EndTime,cte.rt
END

with TimeRanges as
 (  select @Start as StartTime, @Start + @TimeRange as EndTime --StartTime and EndTime
    union all
    select StartTime + @TimeRange, EndTime + @TimeRange
    from TimeRanges
    where EndTime  < @Finish ),


cte as
(
select StartTime as changetime,1 as CC from TimeRanges --StartTime, not SessionStart
union all
select EndTime,-1 from TimeRanges --EndTime
)
select top 1 changetime,rt from
(
select * from cte
    cross apply
    (select SUM(cc) as rt from cte c where c.changetime<=cte.changetime) rt
) v
order by rt desc

with TimeRanges as
 (  select @Start as StartTime, @Start + @TimeRange as EndTime --StartTime and EndTime
    union all
    select StartTime + @TimeRange, EndTime + @TimeRange
    from TimeRanges
    where EndTime  < @Finish )
select StartTime, EndTime,cte.rt
from TimeRanges as TR left outer join
  dbo.Test as Test on TR.StartTime <= Test.SessionStartTime
  and Test.SessionCloseTime < TR.EndTime
where Test.ScenarioID = 24
group by TR.StartTime, TR.EndTime,cte.rt