I first met the Sandia hiring team at a career fair at my college, and I was contacted for an on-campus interview the next day. Three extremely nice ladies conducted my interview, and they took turns asking questions. I only remember them asking behavioral-type interview questions, and a lot of team-based behavioral questions in particular. The women who conducted my interview were very approachable and friendly, and made the interview feel more like a conversation. During the interview they told me it could be a few months before I hear from them because the hiring process is very slow, and to not get discouraged. After the interview, I applied to the position online via Sandia's website, wrote a very personalized cover letter, and sent a thank you email to my interviewers.
After a month, I still had not heard from them so I sent a follow up email to one of the women who conducted my interview. She called me back and apologized, and said HR is still working on it.
A month after that (so 2 months after my interview), HR sent me an email saying they wanted to set up an over the phone "meet & greet" with a hiring manager. I had the phone "meet & greet" a few weeks later, with another extremely friendly person. It was not an interview at all, but him telling me more about the position and answering any questions I had. I sent him a thank you email following our phone call.
A month after the phone meet and greet, I still had not heard back so I emailed the hiring manager to check in. He then told me he wanted to talk on the phone again. He called me a few days later and extended a verbal job offer. A month after the verbal offer, I received an official offer that included the salary.
So overall, it took 4 1/2 months from my first interview until I received an official offer. The interviewers and hiring managers have little control over this timeline as it is the HR process that takes a while. However, they can put a bit of pressure on HR to help speed it along. So my best advice to anyone who wants a position at Sandia is to keep following up with them. If I wouldn't have emailed them every month or so to check in, it seems pretty likely that HR would have forgot about me. Every time I emailed my interviewers or the hiring manager, the hiring process moved on to the next step.