Right now the Gantt charts are basic to the point of being (possibly) less than a MVP tool. For example, there appears to be no way to create dependancies to a milestone, such as a ship date. Why not? This is somewhat related to https://big.ideas.aha.io/ideas/APP-I-2052
We have made ample upgrades to the Releases Roadmap page, and plan to continue making upgrades over time, as we generate feedback from the community.
In regards to your specific request to create dependencies to milestones, it is possible to do this by hovering on the gray dot of the phase of interest and drag it to the associated milestone.
Paul you are right on, thanks!
Quick observation: you can create dependencies between release phases and milestones you (or another user) have added to the Gantt. You cannot create a dependency on the automatically created Release Date milestone (the one that's a diamond shape). It took me a while to realize this wasn't just an issue with the fancy HTML5 UI in Chrome. This may be where the impression that you can't create dependencies on a milestone comes from. I put a quick 20 second video of this here if it helps anyone understand the issue: https://www.youtube.com/watch?v=vWcb_XpA930
Similarly if you add a Feature to the Gantt chart you have to make sure it's associated with a release phase, you cannot create dependencies from it directly, even though the little grey dot appears when you hover over it. The dependencies seem to be only between Phases and Milestones and not between some of the other kinds of things that visually appear on the Gantt.
Hmm, I can't seem to get that connector to work.