Hiring manager has rescheduled our final round three times. At what point do I just walk?

First reschedule, fine, things happen. Second, a little annoyed but whatever. Third one came four hours before the call with no real explanation, just 'something came up, can we do next week.' Recruiter keeps reassuring me the role is still very much open and I'm still the top candidate. I believe her, I think, but I've also got two other things moving and I'm running out of patience to keep clearing my calendar for this one.