Date depencies

Hi Stephen, welcome to the forums! I think what you're looking for is lead/lag time for tasks. Megan's post requests this type of functionality if you want to add your vote for the feature there. I also want to suggest a potential workaround.

Suggested approach:

1. Create a Folder/Project and add all necessary tasks to it. Space the items correctly on the Timeline, so there's 3/6 months in between the appropriate tasks.
2. Create a milestone task to add to the end of the series (this should probably represent the actual event, and be scheduled for the event date). 
3. Create placeholder tasks for the lead/lag times you need to preserve. So for example, create a 6-month task and a 3-month task.
4. Use dependencies to link tasks. For example, create an "Organize catering" task, link it via dependency to a 6-month lead task, then link the lead task to the milestone via another dependency. 
5. Use mass editing to change the status of all tasks in the template to deferred. 

When you go to duplicate your template there'll be an option to reschedule tasks in the template. 

Let me know if that could potentially help!