The schedule management plan includes:

The scheduling methodology and scheduling software to be used on the project;

Establishment of a schedule baseline for measuring against during the monitoring and controlling process group;

Identification of the performance measures that will be used on the project, to identify variances early;

Planning for how schedule variances will be managed;

Identification of schedule change control process

Does this list make you think? Do you currently do any of this for project that you may be involved in$?$ Most PMs just work on the project and hope they meet the deadline. How will you measure schedule performance during the project? What data will you collect? The schedule management plan can be formal or informal, but it is part of the project management plan.