As the title says, archinstall hangs on "Waiting for time sync (systemd-timesyncd.service) to complete." during install IF NETWORK DO NOT ALLOW NTP TRAFFIC TO GO OUT.

It do not timeout as expected.

The only way I found to do my installation was to open another SSH session and:

systemctl stop systemd-timesyncd
nano /etc/systemd/timesyncd.conf
<edit file>
NTP=<my internal NTP server>
<save file>
systemctl start systemd-timesyncd

Then, installation proceeds.