timer.nix

{
  systemd = {
    timers.foo = {
      wantedBy = [ "timers.target" ];
      partOf = [ "foo.service" ];
      timerConfig.OnCalendar = "minutely";
    };
    services.foo = {
      serviceConfig.Type = "oneshot";
      script = ''
        echo hi
      '';
    };
  };
}