Flash boiler question

Theoretically, if one had an MLT (cooler) preheating, then ran that heated water through the boiler (ala Brewpastor, and others) to hit strike temp, it wouldn't take much time at all, would it? Yes, I do realize that it would take a close eye to watch the temps.

Also, using the remaining preheat water, I was thinking that could be run through the boiler to hit the sparge temp. Again, due to the already heated water, it should be fairly quick. I am of course comparing to the times posted by the builders of these boilers who started with 60* water.

I'm reading two different questions here. One is related, I think, to the idea of preserving MLT preheat water rather than wasting. The other is related to using a flash boiler to accomplish that goal.

You actually don't have to waste the preheat water. I never did. If you calculate a necessary strike temp of 166F for example, add the strike to the cooler at 190, close the lid for 5 minutes, then open and stir. If you're still above 166F, stir a bit more until you hit 166F. Dough in.

Well, actually I was thinking more of the preheat water in my HLT cooler. I would like to preheat it, then run the water through the boiler to bring it up to sparge temp. I have one pot and one burner, yet would like to start the boil during the first running. The whole point is to get my setup efficient energy wise.