Not to argue, but some observations with the nitrogen cycle in aquariums vs. ponds if a definite "it depends".
Due to many mistakes as a kid introducing fish far too soon into an aquarium, I have learned to be anal about testing for cycling a new body of water. I did it for many aquariums, the 1/2 acre pond, and now a lined 20x22' garden pond.
In my big 1/2 acre pond, the cycle appeared to begin almost right away, as soon as the first raindrop splashed in the mud. I couldn't even measure it with a standard aquarium kit. The cycle likely completed when there was just a few inches of water standing in the bottom. The bacteria already present in the soil, and "dust" in the air is a major kick-start to the process compared to an almost sterile environment of a plastic/glass container with a brand new filter system indoors. I doubt nutrients stand much of a chance of cranking out toxic ammonia in a pond unless there is a huge inrush of cow leavings or fertilizer as the pond fills. That would be a huge obvious problem.
A new pond basin has almost no nutrients typically, but perhaps not always the case in a fertile environment with ground runoff. But I highly doubt the initial ammonia cycle in the pond nailed his fish, way too long of time elapsed before they were added. If it had, the pond would have had an obvious smell to it.
If damage were caused by ammonia, it could be related to new nutrients in the water column from initial over-feeding and nearby fertilizer runoff causing a quick change in water quality. Perhaps you could call this a cycle, but not quite the same thing. This could happen any time in a pond or aquarium's life by adding decaying matter or fertilizer into a BOW that overwhelms the ability of minimally established life to break it down safely. i.e. a lot of dead fish.
One of the tricks I employ with a new aquarium is to take filter media from an established aquarium, even from the fish store, and jam it in the new filter. The settle time goes from more than a couple of weeks down to a couple of days. I still wait a couple of weeks to introduce fish just to be sure. Pond basin soil and nearby topsoil is like the soggy, nasty filter media I jammed in a new filter.
I expect my new lined pond to take a couple of weeks to safely cycle, even tough I added a little topsoil to the bottom to kick-start it. There isn't enough surface area to host plentiful bacteria to deal with fish just yet. More plants and pots of soil and gravel need to be added in. So far, the first spike of ammonia has yet to even show up, but I just half-filled it yesterday and threw in some already established lilies and iris from the old pond. I may have put a little too much soil mixed in with the gravel, it is kind of murky.
I would love to throw in fish before it's ready so I can control the skeeters that will surely get there first! Goldfish can take the cycle, barely, but they stink at eating skeeters. The plan is to put guppies in to start, knowing full well they will kick the bucket come fall. Just curious to see how quickly they will reproduce. Then comes the fun next year to track down our native little fish to put in there, just for curiosity and too small to eat the frogs.
