If you are updating the Schedule’s Start and/or End time and manual changes have been made to individual Tasks on this Schedule (e.g. through the Task Service Time option), the system will notify you of this and give you a choice between overwriting the manual changes or keeping them:
If you choose to overwrite them, then the new Start/End time will apply to all Tasks on this Schedule. However, if you choose to keep the manual changes, the new Start/End time will only apply to Tasks that were not previously manually updated.