Currently you can only select a single change marker at a time. I could see a use case where being able to select multiple would make sense. For example, code deployments could take a longer duration of time, such as 15 minutes for example. A user could create custom events such as code deployment start and code deployment end. Then if the ability exists to select multiple change markers, they could easily see the start and end in the graphs to identify the impacts on the database during the entire code deployment.