How scheduling and leveling work
The Task information inspector's Schedule method indicates how OmniPlan should determine when a task is to occur in the project.
By default, new tasks are scheduled as early as constraints allow. This means the task is placed at the very earliest time possible, taking into consideration start and end constraints, and dependencies on other tasks. Resource availability is not taken into consideration, so resources may end up overutilized.
These tasks are scheduled as early as constraints allow:
If you manually set the date for a task (by typing it in the Task Information inspector, or dragging a task bar in the Gantt chart), its scheduling changes to on specified date. A task scheduled in this way will remain so unless you select it and click the Schedule Reset button on the Task Information inspector. Then it reverts back to scheduling as early as constraints allow.
These tasks are scheduled on a specified date:
When you level the project, OmniPlan rearranges tasks which have resources assigned, to make sure no resource is being used at more than 100% of its availability. Tasks moved back by resource leveling have their scheduling method changed to by resource availability. When viewing the critical path, a dotted dependency line indicates a "resource dependency" between the task which gets access to the resource first, and the task which waits on the resource.
These tasks are scheduled by resource availability:
During leveling, OmniPlan has to make an educated decision about which task should get access to a resource first, and which tasks should be pushed back by a resource dependency. In judging which task to put first, the following criteria matter, in this order:
Requirements to end by a certain time, such as locked end dates, constraints, or being a prerequisite to a task with such a requirement.
Task Priority, as set in the Priority column of the task outline.
Position in the task outline; tasks with lower ID numbers are scheduled earlier.