Prime works by removing chlorine from the water and then binds with ammonia until it can be consumed by your biological filtration (chloramine minus chlorine = ammonia). The bond is not reversible and ammonia is still available for your bacteria to consume. Prime will not halt your cycling process. Furthermore, Prime removes chlorine and chloramine (even in high chloramine levels), and detoxifies ammonia and nitrite. Provides essential ions and stimulates natural slime coat. Prime also detoxifies any heavy metals found in the tap water at typical concentration levels. When used during cycling, Prime enhances nitrate removal and does not cause a pH drop or overactivate protein skimmers. Great for setting up new aquariums, or when adding or changing water, or to remove nitrate.
Not sure if I answered your question, so let me know if I didn't.
I do agree with Alasse, by liquid testing the water you will know how much water to change. That is, if the ammonia is very high (1.0 ppm or higher) change about 40%, if 2.0 ppm change 60% or until the water test reads back to 0 or nearly so, understand? The key to water changing during cycling is, to test before the water change and then test after the water change (same thing goes for nitrite).
Depending on the tank, it will take about 4 to 6 weeks...the amazing thing about cycling is, after the ammonia starts to drop to 0 as the nitrite rises, you will test one day and bam, out of nowhere, the ammonia and nitrite levels will have dropped completely to 0, then you will know the tank is cycled.
The tetras you are using are hardy enough to withstand most chemical fluctuations - when I first started to cycle my tank back in May 2008, I used 2 zebra danios which are similar to tetras, so there is no problem in this regard.
Let us know how it goes. Cycling a tank is a rather interesting experience because there is anxiety and then out of nowhere, the cycle completes itself overnight.