Not quite as long as it took Adi Shamir, but long.
On average it takes about 14 weeks to get a visa, but on occasion it has taken many many months.
I've done the calculations, the worst-case scenario for the full process is 32 weeks. It's never actually taken that long, but it's not been far off.
I remember having to explain to Microsoft that they needed to write a sponsor/supporting letter (for the US embassy) more than half a year in advance of any potential visit to Redmond that I'd be working at. As this was for DAC (Developer Advisory Council) meetings that Microsoft only scheduled a month in advance they found themselves in a dilemma over this. Thankfully they agreed, and their legal department would author letters that a meeting would likely occur requiring my attendance, but it was always a slog of a process.
For those wondering, I was shortly married to a US citizen and I speculate that this triggers some flag or signal that makes them think I want to stay there (I don't). I also have an interesting past, having been homeless for a while. Who knows though, the system doesn't supply answers. It's a black box process.
It's a nightmare process that doesn't end when you have a visa. On arrival I experience the joys of "secondary", and being sat in a waiting room for many hours before a 10-second interview in which they let me go my way.
Every part of the experience is a miserable one, always with the threat of an axe over the visit.
The vast majority of the time I have been invited, or had opportunities to visit, I just do not choose to visit the USA.