my question is this: when you give SS + y days... you do not know how well the predecessor will proceed in those y days, which would enable the successor to start. how do you solve this problem?



also,

even if you just gave SS, you still dont know how well the predecessor will proceed after starting. for example, the sucessor may still depend on predecessor even after starting even though it just may have SS.

The project plan is a model of reality as best we can project. It requires monitoring and control after the plan is built and updating to reflect the current reality in the project. Project planning is not a once and done exercise. You will need to re-plan and and adjust throughout the lifespan of the project. Microsoft Project is just one of the tools in the project manager's kit.

If you are monitoring progress in the project and the successor cannot start as planned - revise the plan.