First, what are you measuring your heart rate with? If it’s without a chest strap, then I would disregard what you’re seeing. It won’t be close enough to train with. A Fitbit, in particular, isn’t designed for proper endurance training. (Or do some Fitbits come with chest straps?)
Second, the test has to be continuous at a constant pace. That’s why we recommend using a treadmill. Breaks at intersections will be too long.
Third, we’ve moved away from using the nasal breathing as an indicator of aerobic thresholds. It really only works with athletes with a long history of endurance training. It’s more reliable to use the drift test.
Fourth, the be-able-to-have-a-conversation rule of thumb is during activity, not after stopping.
Fifth, I would get a heart rate monitor with a chest strap and re-do the test on a treadmill.