You should have dumped the entire bottle into the tank as soon as you unsealed the bottle. Once unsealed, what's left in the bottle will quickly lose its effectiveness. How big of a bottle did you buy? It is recommended to get one that is rated twice of your tank size for quicker cycling.
Do not do any water change for the next 24~48 hours to let the bacteria spores to settle. Most of them will end up in your filter media where they are supposed to be.
From your readings, it started to work. Tetra Safestart probably provides equal amount of both types of bacteria. The amount of ammonia converted to nitrite was also converted to nitrate. That's probably why you saw no nitrite yet, because the little nitrite the bacteria produced are now nitrate. Give it a few days to see more changes. Be patient.
