The CCC Project Progression Policy explains that each project accepted by the CCC should have a growth plan to track its progress towards the Graduation Stage.
A "growth plan" is a written set of growth goals and a written set of actions intended to make forward progress towards those goals. The growth plan does not need to have a fixed timeline.
The growth plan is reviewed as part of the project's Annual Review Process.
A project's growth goals are, at minimum, the CCC criteria for achieving Graduation Stage.
As a bit of history, the notion of project "incubation" and "graduation" were introduced by OpenStack and have since been followed by CNCF and other organizations, but the exact criteria vary by organization.
Objective criteria for graduation are preferred rather than subjective criteria. Similarly, any additional growth goals should be objectively measurable.