The main reason I don't like timestamp based version schemes is that it makes builds inherently difficult to reproduce.

I wrote some code for a specialized piece of equipment earlier this year. One of the requirements on this equipment is that all package installs contain a unique version string (ie. you can't install the same version twice). So I based build versions on git hash and timestamp. This turned out to be a problem because it made it impossible to reproduce builds without hacking the build system clock. So I switched back to semver for releases.