Perhaps something like this?

CREATE TABLE #SomeClarionValues (DATEOFACCESS int, TIMEOFACCESS int)

INSERT INTO #SomeClarionValues

VALUES (78439,1),(78439,69087),(78439,40001), (75247,7511378),(75247,8630000)

SELECT

ClarionConvertedToDatetime=DATEADD(MILLISECOND,(TIMEOFACCESS-1)*10,DATEADD(DAY,DATEOFACCESS,'1800-12-28T00:00:00.000'))

FROM #SomeClarionValues

DROP TABLE #SomeClarionValues

Cheers!

EDIT: I had mistyped and put a couple identical rows in the temp table. Not a big deal, but was a bit silly, so I changed the duplicate row. I also changed some of the times to show a greater range there.