can a map + regex be used to generate variables for YYYY-MM-DD-HH?

[newnovice]

Where I am going with this is - I want to write error & access - logs out
with the 'YYYY-MM-DD-HH'  suffix. So i need these variables.  

The 'if' statement is not allowed outside the server{} - I am at a loss due
to this. Please con you show me some examples of how to set these variables
with a map regex? 
I can have 4 seoerate maps to get it done - doesn't matter.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,254210,254232#msg-254232