The way I interpreted the rules, the tank has to be "operational" by the end of April. I take that to mean that the system must be filled and running (lights, pumps, etc.), but not stocked.
In fact I recall that the rules encourage photos of additions along the course of the contest, so I'm guessing that my (as yet) unstocked tank is OK.
Another way of looking at it is that it would be irresponsible for any of us to just cram a bunch of livestock into a tank to make a deadline.
I, for one, am taking it slow -- I want this to be a successful setup. If I end up being somehow ineligible for the prize(s), so be it. I'd rather have ti running well, than fast.