A million bacteria weigh 1 mg or so, or 1 ng per bacteria. They double every 20 minutes.
The mass of the Earth is about 6x10^24 kg, or 6x10^36 ng.
If we start with just a single bacterium wieghing 1 ng with a doubling time of 20 minutes we can arrive at the mass of the Earth in bacterium after about 125 doublings. That's just a day and a half. Even if we allow for a much slower doubling time, the Earth can not be more than a few weeks old according to CrazyDiamond's math.