I had an agent reference the 3 hour rule recently on a domestic schedule change and would not even allow a change to an earlier flight on the same day without repricing the ticket. Had a YYZ-YYC where the flight got moved ~1 hour later. I was OK with earlier, but not OK with later, so I called to ask to be moved to the earlier flight. Agent said that because the flight change was <3 hours, it would have to be a voluntary change and would need to pay fare difference at the current prices. I asked them to escalate and they put me on hold and came back and confirmed that they can't deviate from the 3 hour policy and if I wanted to switch to the earlier flight due to the schedule change, it would be a voluntary change with associated fare difference. AC was being unreasonable IMO so I just cancelled the ticket.