definative way to place secs from epoc into timestamp column

I give up.  I have STFW and STFM and still do not feel like I have a
good way to update/insert into a timestamp w/o TZ column with an integer
representing seconds from epoch.  I am adding functionality to a php app
that does a fair amount of work with time and am currently using
abstime($timestamp). $timestamp is a php timestamp.  I found this on the
web somewhere since I find no reference to a function abstime.  There is
significant hits relating to abstime in the docs but it all seems to
refer to an internal data type of low res time data.

Help.  I would really like to do this in the most efficient way possible
but would like it be not likely to break in future releases.

Bret