How long from the time symptoms occur does it become obvious someone has lung cancer?

Depends: Many are diagnosed after only minor or unrelated symptoms and have very early stage disease. Some less fortunate patients have no to minimal symptoms and are at an advanced stage when diagnosed. A lot of it depends on how soon an imaging study is done after symptoms occur. Some are discovered incidentally while looking for something else due to an imaging study being done for unrelated symptoms.

Very soon: With symptoms, history, physical, x-ray, ct scan and biopsy should follow quickly! while other conditions can mimic, biopsy, sputum cytology, and histologically confirmation make the diagnosis.