- How quickly can you trigger it?

Immediately with a breath (as in start inhaling, it happens). Without a breath, maybe 5 seconds or so?

- Also, have you felt it as in waves going up and down? or just located in same place ?

It's all over the body, although I can focus on just one part of the body and do it there, but that takes me a little longer. (We're still talking about seconds here though. Maybe 20?)

- And lastly, does it have any health utility?

Maybe? Haha, hard to say. If anything probably indirectly, since this has come from a meditation practice, and meditation itself has numerous documented/studied health benefits.

I've been able to do it since I was a young child. One method is by activating the tensor tympani muscles and tensing the front of my neck from my jaw (while making a frowning type facial expression - aka make yourself look like a cardassian) - that's the best way I can describe it. There's another way that involves tensing the base of my skull. I can also move my ears, so I wonder if being able to move that muscle plays into this.

I've been able to do this since I was young. For me, I can trigger it instantly. It's mostly very relaxing. Triggers a yawning response if I do it repeatedly. I think I actually learned it by forcing myself to yawn back then. Feels mind clearing too.

I experience the same, just did it in fact! My ears popped (without yawning) and I didn't realize they needed to equalize but damn if I don't feel more alert now that that's done.