Fishless cycling takes time, anywhere from 2 to 8 weeks (various water things affect this) because the bacteria have to establish themselves. I have never done a fishless cycle, and would never bother. I have always cycled with fish and plants, and Ill explain how and why. I'll begin with some basic info that I realize you (MM) know, but this thread will be read by others and some of them will likely be beginners and I am one who firmly believes that the reason behind things is important in order to understand why things occur and why we do this and that so we are better able to care for our fish.
Fish constantly produce ammonia through respiration. Ammonia is also produced from urine and through decomposition of solid waste, plant and animal matter. Ammonia is highly toxic to all fish, and it is present from the first moment a fish is placed in a new aquarium. There are two ways, and only two ways, to effectively remove this ammonia: bacteria and plants. First the bacteria.
When ammonia is present, a bacteria called nitrosomonas automatically appears (in nature and in our aquaria) to feed on the ammonia and thus convert it to nitrite. Nitrite is also toxic, though slightly less so, and a second bacteria appears to feed on the nitrite and convert it to nitrate. This second bacteria used to be thought to be nitrobacter, but a 1998 paper documented the findings of a group of scientists led by Dr. Timothy Hovanec who determined that nitrospira was the bacteria responsible; subsequent writings frequently mention both, as some believe both have a part to play. Whichever it is, the toxic nitrite converts to nitrate which at reasonable levels is non-toxic to fish. Nitrate is easy to handle, as it can be removed (diluted) with partial water changes; in a heavily-planted aquarium it is almost non-existant as I'll come to momentarily.
The process above is termed the nitrification cycle, and aquarists use the term "cycle" referring to this three-stage process. It takes time to establish the afore-mentioned bacteria. Nitrosomonas bacteria appear within 5 to 9 days after ammonia is present, and nitrobacter in 10 to 15 days after nitrite is present. It also takes time for these bacteria to multiply. They do this by binary division, which means each bacterium divides into two new bacteria. In optimum conditions (temperature around 77F, pH in mid 7's) nitrosomonas will divide every 7 hours and nitrobacter every 13 hours. This occurs constantly provided there is available "food" in the form of ammonia and nitrite respectively; once the bacteria are in sufficient numbers to process the available ammonia and nitrite, they cease to multiply. The tank is said to be "established" at this point; this means that the nitrogen cycle is in balance for the bioload present at that time in the aquarium. If the ammonia or nitrite should decrease, the bacteria will die off accordingly. There is consequently always sufficient bacteria present to handle the nitrification--provided something does not occur to affect this process.
Fishless cycling takes time because the above nitrification cycle takes time to establish itself. If sufficient bacteria is added with the first fish in a new tank, the nitrification cycle is immediate. The nitrosomonas bacteria consume the amonia produced by the fish and other processes, and the nitrospira/nitrobacter consume the resulting nitrite. The key is to have the bacteria in balance with the bioload. This can be done in two ways.
"Seeding" the new tank with bacteria from an established healthy aquarium is one way. Bacteria colonize surfaces, so any item such as substrate (gravel, sand), filter media, rock, wood, plants, and ornaments that are moved from an established aquarium to the new aquarium will bring bacteria with it (provided it is not washed or allowed to dry). There must be ammonia being produced in the new tank or the transferred bacteria will die off. Note that bacteria do not colonize water, only surfaces in the water. Moving water from an established tank is useless and in fact detrimental. No bacteria are transferred, but urine, dissolved waste, ammonia, and possibly pathogens and whatever else will be introduced into the new tank. And the fish in the new tank will supply enough ammonia and waste without adding more.
The second way to introduce the needed bacteria is through a biological supplement. Seachem now make one called "Stability" that is live bacteria. The same Dr. Hovanec mentioned previously developed a method for ensuring bacteria can be kept alive in a bottle, and there are now a few types available. Stability is one, and there is a frozen supplement available in the US called Bio-something; I'm not familiar with it because it cannot be imported into Canada where I live. There is also "Cycle" although this is not live bacteria, as I understand it, but it does work the same; I have used it. API have one called "Stress Zyme" and there are a few others. Provided the bacteria is sufficient in numbers to handle the fish load,
there will be absolutely no stress on the fish other than that related to being netted and placed in a new environment. And no fish loss. But again, it has to be balanced; the fewer the fish and the more bacteria, the better, so it is recommended to put few fish in at the start, and gradually add more. Of course, in an emergency this is not practical. I have previously written of my experience some years ago when I had to tear down my 115g tank (with 140 fish in it) in one day and disinfect everything and use new filter media. I used "Cycle" and the fish went back in the same day to a completely new tank. Not one fish loss. And when I moved the same.
Now to the plants. I mentioned above that nitrate is seldom a problem in a planted aquarium. In my own experience of 15+ years, I have always had nitrates at 5-10 ppm, and I have heavily-stocked aquaria. We often read that this is because plants use nitrates as food. However, it is now believed that the plants actually use ammonium, not nitrates, and in fact cannot use nitrates unless they change them back into ammonium. Ammonium comes from ammonia. In acidic water, the ammonia produced by the biological processes largely changes to ammonium. This is why in an aquarium with an acidic pH (below 7.0) there will basically never be poisioning from ammonia; it changes to ammonium, and ammonium is relatively harmless to fish. Test kits (most at any rate) read ammonia and ammonium the same, so testing the water and finding ammonia above 0 can be ammonia and/or ammonium depending upon the pH. This is still reliable, since the nitrification cycle described above uses ammonia and ammonium so it makes no difference which it is. However, the lower the pH, the less effective the bacteria function; some say that below pH of 6 the nitrification cycle is basically gone, which is a major reason why aquarists are advised to maintain a pH above 6. But that's another topic; back to the ammonium.
Plants require ammonium to photosynthesize, and in acidic water they apparently grab most of it before
the bacteria has the chance. In basic (alkaline) water, ammonia remains ammonia, but the plants have the ability to change ammonia to ammonium themselves. Lest you think this is my idle speculation, it is clearly laid out in an excellent article by Diana Walstad [here's the link Aqua Botanic - Plants and biological filtration
] from which the next info comes. She says, "Plants, algae and all photosynthesizing organisms use the nitrogen from ammonia--not nitrates--to produce their proteins." Ms. Walstad mentions that plants probably also use nitrite by changing it back into ammonium in order to make full use of the available food that they need to grow. The main point though is that planting an aquarium heavily at the beginning and then adding fish basically ensures that the fish will again experience no stress nor ill effects (poisioning) due to ammonia or nitrite. The plants consume it and use it. Ms. Walstad says that she has always set up new aquaria with plants and fish the first day and has never had an issue with ammonia or nitrite. She also suggests that there is no need for canister filters in a planted aquarium, only filtration sufficient to create a suitable current of water. The plants do the filtration, and the bacteria that colonize their leaves far outnumber the bacteria in any filter. Dr. Ted Coletti makes the same point in his article in the June 2008 issue of TFH.
In conclusion, the best, easiest and safest way to establish a new aquarium is to plant it, add some fish, and add bacteria. The latter may be "overkill" with the plants, but it can't hurt the fish.