Stretch marks timing

I am now almost 37 weeks and so far don't have any stretch marks. My 25 lbs of pregnancy weight gain has gone almost entirely to my belly so I have quite the bump. I have been moisturizing like a crazy woman and hope that will carry me through the last weeks before baby arrives but even though it is a shallow concern, especially at this point of pregnancy, I really would be bummed if stretch marks popped up now. When do stretch marks generally appear? Am I probably in the clear or do they come on during the last few weeks of growth? Thank you!