I'd guess 10 minutes up to an hour on modern hardware, say a new mac studio. That would be in lightroom - I'm guessing they're using optimized software for this though.

Taking the actual pictures takes at least couple minutes. The Sony A1 can take 50mp shots at 20 fps - pretty amazing. That's (conveniently) 1 gigapixel per second. So minimum 2 minutes to capture this entire image. Add at least a second between shots for the robotic housing and we're talking 4+ minutes.

Could certainly be used to capture most of the faces in a huge crowd.

They do crowd shots like this quite a bit at sporting events and whatnot. I am in this one haha: http://gigapixel.panoramas.com/superbowl/2013/

“This photo was probably created over several weeks, but that being said we could run a simple version where it runs 77 photos at 70mm to create a 2.6 gigapixel photo and that takes 15 minutes,” Cury explains.

https://petapixel.com/2021/04/27/this-120-gigapixel-photo-is...