So am getting this " Time measurement data not available" error everytime i go over 4800mhz with my 2500k,

so is this a bug? or i should be worried about it?

http://www.3dmark.com/3dm/2701912

If it happens on Win8 it means that you are affected by the downclock bug. On Windows7 it could also mean you tweaked the OS too much or your clocks were unstable. Happened to me aswell. Personally I would say it's not a problem

"Time measurement data not available"

 

Means that SystemInfo process that is tracking the timers crashed during the run and could not record the timers at the end of the benchmark. Usually this means your overclock is not fully stable. Note that if you get this error on Windows 8, it means "we can't tell if your result is affected by the downclock bug or not". On Windows 7 it means "we can't tell if your result is affected by some fairly obscure BIOS level "tweaks" that mess the timers". It does not automatically mean that the result is invalid, but it also means that the built-in timer checks are not present for this result, so it MAY be invalid, can't tell.

 

"Time measurement data inaccurate"

 

..means that timers were properly recorded and they are off - something is causing different timers in your system to be out of sync. Most commonly this is due to the Windows 8 downclock bug. Result with this error is definitely invalid.

I also got this error sometimes on win 7^^

I ignored it like der8auer said