Convert seconds to datetime in SQL Server

Given your example, try this:

select DATEADD(s, dateTimeInMilliseconds, '19700101')

Informative time span string:

declare @seconds int = 93825

convert(varchar,(@seconds/86400)) + 'd:' + format(dateadd(ss,@seconds,0),'HH\h:mm\m:ss\s')

Result: 1d:02h:03m:45s