Like the question says.

The game is installed on a SSD. The download of the current patch took 5 minutes but for the past 45 minutes, I've been looking at the words "Less than a minute" for the remaining duration of the patch

The write speed of the SSD is not all - when installing a game or a patch, your system decompresses all the installation files, and that process is very much CPU dependant. So it may be your CPU is not fast enough to unpack everything at a desired speed.

Also, the GoG installers is known for compressing everything twice. The second time gives like 10 % smaller filesize, but still takes twice the time to unpack.

Personally, I just watch Youtube on another monitor or go grab a snack while the patch or game installs itself.

EDIT:
Are you installing from and to the same SSD? If you have downloaded the files on the SSD, and are trying to install from that SSD to another folder on that same drive, you are really killing the performance and slowing down the process.

I also have a NVMe SSD for my games, and I always download the installers into another physical drive (even a hard drive), and install from that and to the SSD.

I'm having the same issue with Cyperpunk 2077 but not with other games inside or outside of GOG, typically. A handful of games exhibit anomalous properties, and Cyberpunk 2077 gaining almost zero progress updating for over an hour is one such anomaly. Sometimes these just happen once, but sometimes it is a trend with the game. This one has been a trend with CP2077 updates on GOG every time.