I personnally try to make the most of every signle turn, being a micro-mgmt freak...
Turns when i'm fully militarily-engaged can last about 2 hours or even more...
A Battle lasts almosts 20 minutes and sieges may last as much as 30 minutes with the clock on...
I like to make the most of my diplomats, spies and so on...

PS : One thing that buggers me is why can't a diplomat try to negociate with more than one faction at a time like it did in RTW... Seems logical that you could have a MTW2 "G-8" with plurilateral talks....