How soon can marijuana plants start budding?

6-8 weeks, generally. Might be more, might be less, depends on the plant.

for indoor grows, they start flowering shortly after they have been switched from an 18/6 light cycle to an 12/12 light cycle. This happens because the lighting simulates the oncoming of winter...

Mine will in a week or so.

The cannabis plant begins flowering when it senses the light cycle is beginning to have more darkness and less sunlight and begins budding to pass on its seed since they know there going to die...

in door= as soon as you cut the hours to 12 out door= around mid to late august