Leaders may need to know some specific dates for some specific purposes. Responding to that need by demanding your methodology deliver a schedule for everything in case you need it is lazy and wasteful.
If your engineers are part of the same team, working on the same business goals, they'll be glad to contribute what you need to the decision about whether to announce at conference Y, and may even be able to suggest relevant aspects you haven't thought of.
If your engineers are part of the same team, working on the same business goals, they'll be glad to contribute what you need to the decision about whether to announce at conference Y, and may even be able to suggest relevant aspects you haven't thought of.