Thanks for the feedback Marc, but I think you have misunderstood what I am looking to do.
The [+date+] parameter is controlled by datesource + dateformat, If I add [+pub_date+] as is, it doesn't get rendered as a readable date.
In this case the "datetime" needs to be converted to a machine readable format, I don't know how to do that, and that is my question - how to convert that.
With Phx you could use
[+pub_date:date=`%b %d, %Y`+]