Use imprecise times, because the time to build depends on your computer

Co-authored-by: Camelid <37223377+camelid@users.noreply.github.com>

Author: Joshua Nelson

src/building/how-to-build-and-run.md

@@ -251,4 +251,4 @@ everything up then you only need to run one command!
 ```
 
 `rm -rf build` works too, but then you have to rebuild LLVM, which can take
-a long time (on the order of a half-hour).
+a long time even on fast computers.