They are probably true.
Using an i5 @4.3GHz it takes 2.5/3 hours to build. To test changes you must set up a compiler cache or it's going to take forever.
20 minutes sound like a dream, I don't know why it's so slow for me. Maybe because I'm using Nix to build it and the source is on an SSD. I can't use tmpfs because it doesn't fit in memory without adding swap.
