Your SharePoint DR plan should be considered a living document, which means that it will continue to evolve over time as your farm continues to grow and new technologies are introduced into the environment.
Over time, you may find that budget constraints that at one point limited your RTO and RPO goals may no longer be a concern and your RTO and RPO goals can be adjusted accordingly, as new funding is made available for things such as a standby datacenter.
You should schedule periodic reviews of the plan and adjust the plan as necessary. It is important to continue to test your SharePoint DR plan as it evolves over time.
For example, you should plan to review your SharePoint DR plan at least once a quarter. You should review all aspects of the SharePoint DR plan, including your recovery targets, RTO, and RPO.
You should plan on performing a full test of your SharePoint DR plan at least once or twice a year, depending upon the size of your organization, number of systems...