You reach graphical target (DM mostly) in 31 seconds.
networkd-wait-online takes 30.5 of them.
If you disable it, usually nothing goes wrong.
Disable the service and reboot to check.
If something breaks (on your system), re-enable it (in TTY, if you get in trouble).
Arch is for the brave! 
No risk, no knowledge, no gain. 
Ask elsewhere, if you don’t trust. 