Digging back into my memory here.
In general, advertising takes a minimum of three months to see the benefits. Once sales start rising, newbies tend to stop advertising because, well... they have sales. The problem is that it's a bell curve. Advertise for 3 months, start seeing sales, if you stop advertising, three months later, you're sales will be zero again (add salt to this).
All industries are different, but in general.
This is Marketing 101. While it can be boring as shit, I highly recommend putting on your big boy pants and taking an Intro To Marketing college course. I'm sure you can find a free one online. You can even just audit the course so it's way cheaper. You just won't get the academic credit for it.