Just got Blackened Naaru Silver on our first M'uru kill. Went to BL to test it out. So basically the proc consists of 2 procs. Battle trance that is the actual proc, has a 45sec hidden cd and Combat insight thats the stacking buff. It procs a second after Battle trance all the time and within around 5seconds its fully stacked up for a rogue.
So here is the uptime for it, around 40%
And here is the log for the testing if that can be used for the spreadsheet:
http://rapidshare.com/files/114229690/battle_trance.txt.html