date ranges in view filter criteria Drupal 7, Views node to be selected on date range.

I would like to have my view only return nodes that were created last month, no matter when I run the view this month.  So as it's the middle of January, I want all nodes created in December last year, and next month I want all of January's

So the dates would be between first day of last month and the last day of last month.

In php I can use:

echo date('Y m d', strtotime('first day of last month')) 


and 

echo date('Y m d', strtotime('last day of last month')) 


to get the correct date range.

However, in Drupal, the SQL does not create the correct ranges.

Viewing the view and sql logs at 11:55 on Jan 16th 2013 I see :

(node.created &gt;= 1358337264-2678400


which works out as 2012-12-16 11:54:24, so it is a month ago, but not the first day of that month.

Any thoughts.
If possible, it might be beneficial to create a separate Date field for your content type. I often find that if I need to do custom filtering in a view, filtering by the date field instead of node post date is much easier. Being able to collect different granularity such as day and month can be helpful also.