How to typecast an integer into a timestamp?

Hello!

again quite a stupid problem i regularly run into....
and that i still haven't solved yet...

again i used a type timestamp to keep a track of modification time, and again it gets stupid and confusing.....

first of all the errors are labeled as timestamp without timezone, i only specified timestamp....

the data was created as a timestamp with php-mktime, but when sending to the database postgres complains that its an
int,and when i try to typecast it, (with the ::timestamp appendix to the value), that its not possible to convert an
intto a timestamp (without timezone) ..... 

so as usual i would discard the timezone datatype and alter the table to use integer instead, but this time i am
wondering,since this datatype is present, there's surely a way to use it properly? but how? 

please enlighten me!

ciao
Bruno