I have used BIO-Spira in the past. Follow the Directions. Add fish 24 hours after the BIO-Spira unless you plan to use ammonia to feed the bacteria. If you add the BIO-Spira, then do nothing but test you will lose some bacteria as they have nothing to eat and then when you add a full bio-load you've just shot yourself in the foot.
Having said this, you may still discover a large spike. In my case I had ammonia, and nitrite spikes both after using BIO-Spira. I still cycled faster than if I had not used BIO-Spira at all, but I still had a longer fishy cycle than I would have liked. My favorite method of cycling is combining BIO-Spira and Fishless Cycling. Simply dump in the BIO-Spira, give it 24 hours to settle in, then dose ammonia to 5ppm. Check in 24 hours. If the ammoni and nitrites are gone and you've only nitrates left, congratulations, you're cycled. If you still see high ammonia and or nitrites, congratulations, you've just saved your fish from a lot of anguish, just keep adding ammonia to 5ppm daily until the bacteria can get rid of it in a 24 hour period, then do a large volume water change and add a full bio-load. Good luck!