If it turns out that the time is stored in milliseconds with a base of 1970-01-01 00:00:00.000, then this code will work.

-- Milliseconds since 1970-01-01 00:00:00.000

declare @TimeMS bigint = 1397750400000;

select

[Date/Time] =

-- Verify time can be converted to datetime

case when @TimeMS between -6847804800001 and 253402300799998

then dateadd(ms,@TimeMS%86400000,(@TimeMS/86400000)+25567)

else null end

Results:

Date/Time

-----------------------

2014-04-17 16:00:00.000

This will do the reverse conversion:

declare @DateTime datetime = '2014-04-17 16:00:00.000'

select

TimeMS =

(datediff(dd,25567,@DateTime)*00000086400000)+

datediff(ms,dateadd(dd,datediff(dd,0,@DateTime),0),@DateTime)

Results:

TimeMS

-------------------

1397750400000

Note:

I just realized this is an old post, but the answer is correct if anyone cares.

It's just a bit of code I had laying around from an old project. 😎