The autologin doesn't require a reboot to work, just issue the following command:
this will restart the server and autologin the user you defined.
here is the "Code" again, i forgott the [daemon], it wont work without:
[daemon] TimedLoginEnable=true TimedLogin=your_username TimedLoginDelay=0
Hey, this still works if you're using Linux Mint Debian with GDM3! Use /etc/gdm3/daemon.conf as your config file.