datepart(year, c.cko_date)

select datepart(year, getdate())

datepart(year, c.cko_date + 25567)

--declare an integer representing the number of days since 1970-01-01
DECLARE @days_since_unix_epoch int = 17674; --2018-05-23
--show the datetime value in UTC
SELECT UTC = CONVERT(datetime, @days_since_unix_epoch + 25567)
--show the datetime value in North American CDT
   , CDT = CONVERT(datetime, @days_since_unix_epoch + 25567) - CONVERT(datetime, '05:00:00');

1970-01-01 00:00:00

SELECT [1ms] = CONVERT(datetime, '2018-05-22 00:00:00.001')
     , [2ms] = CONVERT(datetime, '2018-05-22 00:00:00.002')
     , [3ms] = CONVERT(datetime, '2018-05-22 00:00:00.003')

datetime2