Converting Unix seconds to date

Questions
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1

How would I frame the query to convert from UNIX seconds to the date and time it represents?

For instance, the value 1409855505, translates into 2014-09-04 18:31:45 (UTC).

2

I’m not sure if that’s built-in but you could query for that using the actual definition of UNIX seconds:

3

The Wolfram Language function AbsoluteTime counts the number of seconds from Jan 1, 1900, while UNIX time is the number of seconds from Jan 1,1970.

You can convert pretty easily with the following:

DateList[1409855505 + AbsoluteTime[{1970}]]

which returns your expected:

 {2014, 9, 4, 18, 31, 45.}