Thinking a bit more about it, since MNK Meditation actually takes less time than a server tick to perform, it would be hard to gauge whether it would be worth it any particular instance or not, even if you have 3-4 seconds left on the Demolish DoT. For example, if you use Meditation at four seconds left before immediately reapplying Demolish, but the DoT didn't actually apply its potency in the span of time before you do so, that's going to be a loss regardless.

In terms of gauging the effectiveness of "Meditation weaving" from SSS tests, or even parses without further in-depth analysis, minor gains and losses could also be a side-effect of Deep Meditation/Crit/Direct Hit RNG skewing results one way or another. As Gooner mentioned, there's plenty of time for using the ability in less tentative situations. Also, I miss Fracture too.