Like some of the other answers here point out, the green card process is separate from the L1B visa process, so there is no need to wait for a specific period of time. Actually, I would suggest that you begin as soon as you can because the process can take a long time. Because you first have your L1B nonimmigrant visa, an immigrant green card will change your status and that may be why it seems like you need to wait some time before applying, but the green card application will not be affected by your nonimmigrant visa.
So, the first thing is to determine whether you qualify for a green card. You can qualify by fitting into one of the set out categories, the most common ones being family members of citizens or employees of US companies. If you fit into one of those categories, the family member or employer will file a petition on your behalf. If you don’t fit into one of those broad categories there are still some more specialized areas that you may fit into and in that case you could file a petition on your own behalf.
Also, it is important to keep in mind that US Congress sets a certain number of green cards that can be given out each year, so after you determine that you qualify, you need to make sure there are visas available in your category. If you qualify and visas are available then you can submit your application to the immigration committee who will review it and determine whether you will be granted a green card.
To go back to your specific question, you don’t need to wait to apply for a green card if you determine that you qualify and that visas are available in your category. I would suggest that you speak with an immigration attorney to help you through the process though because it can be tricky. If you are looking for an immigration attorney or if you still have more questions, I invite you to visit. Our legal platform makes it easy for individuals to an on-demand attorney at a reasonable cost. We offer free initial consultations & a satisfaction guarantee.