You can certainly start to plan the sequence of workstreams or activities but if timelines are moving there's little point in putting real calendar dates on those. You could come up with a logic/network diagram for your project if you are using a predictive approach and tell stakeholders if we start on this date, we'd likely finish on that date.
However, as it sounds like scope and approach might be changing too, you are likely more in an adaptive situation where you'd want to first understand what is most important to your stakeholders re: scope, schedule, cost, and then plan accordingly respecting that primary constraint.
What you are describing is often required to establish feasibility, and down-select solution approaches. What you are really doing at this point is exploring your constraints.
You can lay out the overall sequence of events at a high level for different approaches. You may be able to put *some* calendar dates on those flows if you have specific constraints like due dates for certain deliverables. Those dates add constraints to the flow.
Based on decisions such as construction methods, you may know approximate lead times for certain deliverables. Likewise you may know approximately when you will need to add staffing to complete work. This starts to tell you when certain decisions are required, if they are to support an approach, such as when vendors must be selected for long lead items.
Not all constraints will apply to all approaches or apply the same way. This is where you can trade the approaches against each other, and once a selection is made, you have the high level flows and milestones established even if they don't all have dates assigned. Saving Changes...
Sergio Luis ConteHelping to create solutions for everyone| Worldwide based OrganizationsBuenos Aires, Argentina
In my personal experience, Theory of Constraints is the answer to your question. Saving Changes...
