I did five interviews and a project for the last job I didnt get. I'm scheduled for interview number four for a job I'm working now.
When I was hiring engineers I capped it at three interviews, maximum two hours of candidate time.
The reality is that if you know shit about your job, you will know if someone is a good fit in the first 10 minutes. If they suck, you will know it faster. It doesn't take hours and weeks to hire people, you just have to grow a set and be secure that you know your shit.