Is it possible to report on Timeline Activities that are tied to a specific CTA? For example, for an Implementation CTA, it would be cool if we could see all the Timeline Activities that are created from that CTA and then do stuff like sum duration of time.
Pretty sure it's possible to get the report you're looking for here.
If you build a report on the MDA Object 'Activity Timeline', you can add a filter for Source = COCKPIT.
For isolating entries like Implementation CTAs, you might have to add Activity Type(s) and/or Reporting Categories to fit your needs and have CSMs log entries according to how you plan to report on Timeline entries. (Administration > Workflow > Activities and Timeline)
Pele is spot on - you can certainly target the context of the Timeline Entry (Cockpit, Account or Relationship). This is also possible to view via Global Timeline using filters to the criteria you need.
Adding to the above ideas, if you want to report together on CTA and Timeline data then you can use bionic rules to merge ActivityTimeline and CTA data using context type = "CTA" and contextId = CTA Id