Speed upgrade from ISP - DIA INET - 3 hours down

I'm trying to get an idea of what it's like from the ISP side to do something like this. Our original connection was a 100 Mb port, so the speed increase to 500 Mb required a 1 Gb port from the ISP. On my end, I had to move a cable, and set our router from 100 Full to auto-negotiate.

3 hours of downtime on the ISP side as they provision the new circuit. IP's stayed the same. What exactly is happening on their end that could cause so long of a downtime? All the tech kept saying was that their PVC wouldn't provision.

I know things aren't simple, so I'm just trying to get an idea of what the ISP has to do for a speed upgrade.