When setting a Milestone to have a date, the duration of the Milestone task is set to 1 day. This impacts scheduling dependant tasks in the timeline - say I have a milestone to record when two important tasks are completed - the milestone has to be set the day after the tasks are scheduled to end. If I have tasks that are dependant on completion of the milestone - these have to start the day after the milestone is completed.
In reality the Milestone completes on the same day the blocking tasks are completed, and the tasks blocked by the Milestone start on the same day.
When creating milestones in the timeline and moving them around, this behaviour is enforced and confusing/annoying. Milestone tasks should really have zero length duration.
Does that make sense?
2 Likes
Hi @anon40008059, thanks for reaching out 
When selecting a due date for your Milestone, this is not the task duration but the date you expect the Milestone to be completed. You can choose it be completed on a specific date, Aug 4 for example. You can also choose to omit a due date leaving the “date range” as zero as you mentioned. However, this Milestone would not be scheduled in the Timeline without a date.
Does this make sense?
Yes - have observed this. But when the Milestone has dependencies either side, it is treated as having a days duration. If a milestone with dependencies is moved in timeline view, the dependant tasks move as if the milestone was a day long.
And the dependency lines are marked red if the dependant tasks are set on the same day, as if the timings are invalid.
Thanks for getting back to me @anon40008059 with that additional context! I agree that this could be a helpful update to Milestones.
I’ve gone ahead and moved your post to the #productfeedback category to give you and other users the chance to vote for this feature! I’ll keep you posted and let you know if I have any updates