The appropriate phrase I've found to be effective for when someone is wasting my time is "this seems to be out of scope for me right now". It forces someone to

The appropriate phrase I've found to be effective for when someone is wasting my time is "this seems to be out of scope for me right now". It forces someone to justify why this waste of your time is somehow relevant, which they usually can't do. Ex: "I'll leave you guys to finish talking through this one as it seems out of scope for me right now. I'm going to get started on previously-discussed-priority-item." For someone to ask you to remain on the call after that is implicitly saying their discussion is more important than another item that has been agreed to be a priority.