The process in general worked like this:
The candidate is found, either by the hiring manager themself, through an internal referral, or via the internal sourcers/recruiters (shout out to them for being amazing at their job!)
The hiring manager sets up an interview panel, where they recruit relevant stakeholders (in the case of an engineer, this was usually peer engineers and sometimes other managers who that team worked with a lot).
The panel is usually around four hours, with four or five people, including the manager, someone from HR, and some future peers.
If that goes well, then a second panel is set up for round two, also about four hours, which usually involves a Director or VP or two, maybe another higher up peer or sibling team peer or manager, and a higher up manager from HR.
Throughout the day, the hiring manager solicits feedback from the interviewers, usually within 15 minutes of them finishing.
The final decision rests solely with the hiring manager, but usually most of the feedback needed to be positive to move forward. The manager could also stop the process at any time. So if all the feedback was "meh", they could save everyone some time and cut it short.
Out of town candidates would have the both panels set for one long day, or sometimes the afternoon and following morning, so for out of town candidates who got all the way through, it could be pretty grueling.
After all that, if the hiring manager decides to hire you, you could get an offer before you even leave, or within a day or two usually, unless there were multiple people for one position, and then you had to wait for them all (although if you were amazing you'd get an offer anyway and then if someone else was good they would get an offer too).
For me personally, the entire process from first contact to signing offer papers was less than a week, and that was pretty typical at the time.