Pretty long -- first you have to complete 3 rounds of online assessments. First, you have 21 minutes to debug 7 methods, then you have your typical 100 minute coding challenge (which also came with a workstyle assessment), and the third round was a workplace simulation. After the online portion, I had a 45-minute phone interview.
My phone interview experience was extremely disappointing. I have never had such an unprofessional, uncourteous interviewer who explicitly accused me of cheating multiple times. The question he asked was pretty straightforward and common anyway (with only like 2 possible solutions from my knowledge), so I think it's highly likely that an interviewee would write code that resembles the sample solution. Also my camera was on (and my webcam is at the bottom of my screen), so I feel like it would have been pretty obvious if I was typing on a different tab or something. If he thought it was suspicious that I got the answer so quickly, he could have asked a different question or maybe added an extension so I could prove my understanding. Anyway, I hope no other candidates experience such terrible treatment from Amazon interviewers, but I was just appalled by the fact that instead of assuming that I had prepared well for my interview and really knew the concepts, his first instinct was to accuse me of cheating.
He also continued to make me feel uncomfortable throughout the behavioral portion of the interview as well (he just had a consistently unfriendly attitude towards me for some reason), and didn't even let me finish asking questions at the end of the interview. So I'm expecting a rejection, but even if I somehow get an offer, I will not be accepting it.