Hi Marie,
After thinking about this for awhile, I'm with Colin. Where any sealife is concerned, especially invertebrates, stability is just as important as water quality. I've heard many horror stories where hapless aquarist noticed their octopus/coral/fish/whatever getting sick, and changed half the water in their tank- which immediately killed the sick animals. A smaller and more gradual water change might have saved them.
That said, I imagine a difficult scenario to maintain water stability in your tank with an intermittently running pump feeding new seawater. I would opt to use the pump to fill your tank, then let the tank's filtration polish the water- a nice big sump and a W/D system with a skimmer. Fire up that cast iron pump to do your monthly 10% water changes, and that's it.
Whatever the scenario, the only time you're exempt from the 3 month tank cycle waiting period is if you're running a full blown open water system. There's no way to speed it up- the nitrogen compound levels are classically the only thing aquarist worry about when setting up a new tank, but there is a lot more going on in your water than having bacteria break up nitrogenous molecules. A newly cycled tank has just barely caught up, but in that 3 month waiting period, biologicals colonize your gravel, sand, rock and filter, and stability is ensured.
Dr. James Wood wrote a great article on aquarium stability.
http://is.dal.ca/~ceph/TCP/stable.html
Cheers, Jimbo