Actually, it's 3e9 = 3*(10^9) which is about 95 years. So it would be
Here are ways effective programmers get the most out of their precious 95 years on the planet.
It's just a geeky, indirect way to say time:
Here are ways effective programmers get the most out of their precious time on the planet.
Your/their/etc time on Earth is a common expression that means your lifetime. Naturally, in the given text, "the planet" is Earth. The suggestion is that your lifetime is short and that you should make the most of something, like life, or in this case, programming.
95 seems kind of high, so I'm assuming the author just made up a number and that it is not a reference to some work, or joke, or some other thing. I assume that 3e9 just follows the theme of programming.