Although a cancerous tumor may be too small to be visualized with a scan at the time, how long does it take to grow to 1cm? weeks or months?

Growth of cancer: you are talking as if cancer is a one disease unfortunately it is not. the rates of growth vary from one cancer to another and in the same cancer as well. some cancer s are well differentiated other are poorly differentiated so you cannot judge the rate. Usually cancers take months to grow to a measurable sizes rather than years or days. Small cell lung cancer needs weeks to grow to be measured.