If you are already using a timeline to move the instances, you can use the same setup, but also have an array of the ‘syncronization offsets’. It’s just a float array.
Then, on the execute pin of the timeline you can use a foreach loop to move the Z coord of the instances ( using the offset array ).
Tell me if you need more info ( also maybe show your current timeline code ).
It’s very ‘procedural’ though, this method. There a more subtle method that involves spawning empty actors with timelines to control the rockets.