Gringotts getting the kinks out

I'm only basing this on Seth's posts and looking at wait times from afar, but it seems Gringotts is down a lot. I understand that's expected for a new ride. My question is: how long does it take for a ride like this to run with just a normal level of interruptions?

Depends on what you mean "normal" -- look at Test Track, or Mine Train -- they both have lots of daily downtime. I do expect Gringotts to get noticeably better by fall, when they have shorter hours and more maintenance time.