CREATE TABLE #hours (hh int) 
INSERT INTO #hours 
SELECT TOP 24 RN= ROW_NUMBER() OVER (order by object_id)  -  1 FROM sys.objects  

 
CREATE TABLE #input
(
report_time datetime 
, depid int 
)

INSERT INTO #input SELECT '20180215 05:26:12' , 333111
INSERT INTO #input SELECT '20180215 06:26:12' , 42412 
INSERT INTO #input SELECT '20180215 09:10:12' , 31415
INSERT INTO #input SELECT '20180215 22:02:12' , 666999

SELECT 
 report_time  , depid  , hh = DATEPART(hh, report_time)  
INTO #input_hours
FROM 
  #input i 
 

SELECT 
  G.hh 
, report_time = COALESCE([z_report_time], [zz_report_time]) 
, depid =     COALESCE([z_depid], [zz_depid]) 
, '#'
, oi.depid 
, oi.report_time
FROM 
(

 
SELECT  
 H.hh
, [z_report_time]  =  Z.report_time
, [z_depid] = Z.depid 
, [zz_report_time] = ZZ.report_time
, [zz_depid] = ZZ.depid
FROM
#hours h LEFT JOIN  #input_hours ih  on ih.hh = h.hh 
OUTER APPLY (SELECT TOP (1)  h2.depid , h2.report_time FROM #input_hours h2 WHERE h2.hh  <= h.hh ORDER BY h2.hh desc  ) Z /*вниз*/
OUTER APPLY (SELECT TOP (1)  h2.depid , h2.report_time FROM #input_hours h2 WHERE h2.hh  >= h.hh ORDER BY h2.hh asc  ) ZZ /*вверх*/

) G
LEFT JOIN  #input_hours oi on oi.hh = G.hh  /*прост для наглядности */