My bad. This works for per project configuration, but not for global user configuration.
I think it should work at the user config level too:
> If project-, user-, and system-level configuration files are found, the settings will be merged, with project-level configuration taking precedence over the user-level configuration, and user-level configuration taking precedence over the system-level configuration.
It should work for global configuration too, please file an issue if you’re observing otherwise.
(Make sure you’re on a version that actually supports relative times, please!)