Welcome Robbo.
As you have said, when the ammonia and nitrites can consistently process to zero in 12 hours after an addition of ammonia, the cycle is ready and you start thinking about fish.
Contrary to the impression given by Fishyfeet, bacteria do not live only on waste, instead they use the ammonia or nitrites to supply their growth needs. The chemicals each affect the fish in different ways, they do not just burn the fish and damage internal organs. The main effect of nitrites is to deprive the fish of oxygen which can result in nerve damage, not organ damage. Ammonia's first and most obvious effect is to burn the gills of the fish.
You dose the ammonia daily unless you still have some in the water from the day before. When ammonia starts to be processed by the bacteria, the nitrite processors have something to use to increase their numbers. The ammonia stage is often done in 3 weeks or a bit less but the whole process usually takes longer. Once the ammonia processing is going well, you will be unable to measure the nitrites for days or even weeks because it will be too high to measure. When it come back down it will do it very quickly. From that point to completion can easily take another week or two. When we are convinced that the cycle is complete, we do a massive water change, as much water as you can get without destroying the tank decor, and that reduces the nitrates that have built up to a reasonable level for the fish. For details on doing a fishless cycle, I carry a link in my signature area.
As you have said, when the ammonia and nitrites can consistently process to zero in 12 hours after an addition of ammonia, the cycle is ready and you start thinking about fish.
Contrary to the impression given by Fishyfeet, bacteria do not live only on waste, instead they use the ammonia or nitrites to supply their growth needs. The chemicals each affect the fish in different ways, they do not just burn the fish and damage internal organs. The main effect of nitrites is to deprive the fish of oxygen which can result in nerve damage, not organ damage. Ammonia's first and most obvious effect is to burn the gills of the fish.
You dose the ammonia daily unless you still have some in the water from the day before. When ammonia starts to be processed by the bacteria, the nitrite processors have something to use to increase their numbers. The ammonia stage is often done in 3 weeks or a bit less but the whole process usually takes longer. Once the ammonia processing is going well, you will be unable to measure the nitrites for days or even weeks because it will be too high to measure. When it come back down it will do it very quickly. From that point to completion can easily take another week or two. When we are convinced that the cycle is complete, we do a massive water change, as much water as you can get without destroying the tank decor, and that reduces the nitrates that have built up to a reasonable level for the fish. For details on doing a fishless cycle, I carry a link in my signature area.