Installing SharePoint 2013 farm updates takes considerable time: hours, not minutes.
Service applications such as Search and AppFabric consume substantial CPU time, leaving little for the update process. Updates have also grown larger than the product itself: the SharePoint Server 2013 with SP1 installation ISO is 2.62 GB, while January 2016 CU is 3.1 GB.
Combining that update size with CPU-hungry service applications explains why updating one server took several hours.