G. Mark’s Answer
This will be an unsurprising answer. The answer is that it would take as long as it takes to be an engineer. There are many people who are called "engineers" but have none of the preparation or education. One particular example is defining a "System Engineer" as anyone who works on "systems". It's entirely within a person's prerogative to make that claim, but I think it's about as valid as telling people you're a "doctor" because you can distribute Band-Aids. Now, I'm not claiming that these folks don't have a valuable contribution to make much like the person in the sandwich truck coming to the worksite has a valuable contribution to make. But that person is not a "chef". Therefore, if you want to be a "robotics engineer," it would be prudent to get an engineering degree. It may be an Associate Degree or any other engineering degree. Once you are in that curricula, you would look for classes that cover robotics itself. I would also recommend Machine Learning or any other Artificial Intelligence-related classes. But to contribute to a robotics project of any kind, it would be a good idea to spend some effort on that background. Plus, it will likely be a lot of fun.