Project Task Planned end dates set outside of Project schedule update to match Planned start date value, converting it to a milestone taskIssue OOB, a Project Task's Planned Start and End dates will not use hours outside of the Project schedule. A good example of a default Project schedule that would be outside of the schedule would be the weekend. If you were to set your Planned start and end date values to the weekend, even if they were different by a few hours, on update, the Planned end date value will snap to the Planned start date value, making a Planned duration of 0. This also converts the task to a milestone task.CauseAlthough this is the expected behavior, you can select 'Allow dates outside schedule' in the Details section of the child Project TaskResolutionNavigate to the Project Task you wish to set dates outside of the Project ScheduleScroll to the 'Details' sectionCheck 'Allow dates outside schedule'Save/UpdateNow you can set your Planned start/end dates to dates outside of the schedule and the dates will not update to be 0 second duration