This Quartz plug-in displays the latency for the second Mind Flay tick to facilitate casting MF2 (clipping the last tick).

The latency bars will update when pushback occurs. You will always lose at least the third tick in this case, so you're actually forced to cast MF2. A good example is Sarth3D, where you'll continually suffer pushback because of Twilight Torment.

I also added another spark. While you cast a spell, you can send the next spell to the spell queue. There's a slight delay between stopping the current cast and starting the next (queued) cast. The new spark will show you when exactly you sent the next spell. Normally this spark should land somewhere in the red latency zone.

The plug-in is for Quartz r10. You can get it from curse (the version on wowi is r7, not sure if it's compatible).
It requires Quartz_Player and Quartz_Latency to be enabled.