... Either I am completely misunderstanding what you mean, or I was not clear enough in my question.
Example: I have a fort with a magma chamber far on the other side of the map. I don't want my guys wasting time running all the way down there, and I want to keep my fort centralized over near my farms. The other reason for the farms being there is that the sand is there. Thus the magma chamber is on the exact opposite side from the sand, which means if I am to do anything, I would require a lot of hauling.
I heard somewhere that magma will not cool so long as it is in some way connected to the magma chamber. Then there was the comment above, "If you can shut off its connection to the magma source, it will cool by itself.", which, assuming I am not horribly misinterpreting it, confirms this fact.
Thus my question: Does the distance I channel the magma truly not matter, so long as it remains connected to the main vent. or is across the whole map too far, likely resulting in the magma cooling?
And a new question: So depth controls it: if I do this channeling on the lowest Z-level of my fort, it then will take much longer to cool, but will eventually cool?
And another new question: Bridges currently act as aqueducts are supposed to (if they worked), holding 7 magma and not overflowing into the surroundings (or in this case chasm) since it won't 'flow up'?