0 - 2 of 2 tags for Standard Deviation

I am stuggling with how to create standard deviation on timestamps.  I have tried breaking the the timestamp apart as an integer calculating and putting it back together but my issue now is how to take my integer and reconvert to a time?
Here is a sample of the sql can someone assist?

DROP TABLE ajEvents;

I'm getting the "SELECT Failed. 3706: Syntax error: Data Type "response_tm_sec" does not match a Defined Type name." error when I run the following SQL on SQL Assistant:
select min(response_tm_sec) min_response_tm
, average(response_tm_sec) avg_response_tm
, max(response_tm_sec) max_response_tm