How do I get the (date)timestamp since last cron run? I'm building a module but am stuck..
I need the timestamp from the previous cron as I run a hook_cron job so I can check which nodes are new and email those.

So I need the date/time stamp from the last cron run but how do I get there'?
A UNIX timestamp of the last cron run can be fetched with:

variable_get('cron_last');


If you need to, you can easily manipulate a UNIX timestamp with PHP's date function.