> Last I heard, your employer can apply for a greencard after 5 years on a visa. You can then become independent after a grace period with the sponsoring employer. 6 months is typical.
Having gone through L1 process myself I don't believe the 5 years until application is an official requirement. L1 visa itself maxes out at 5 years, so filing for the greencard with the work permit(EAD) at 5 year mark will leave the employee unable to work until the work permit is granted. I have seen cases when companies would file for a greencard almost immediately after transferring the employee on L1 visa.