As explained in our documentation about [[the fingerprint of *Tor Browser* in Tails|doc/anonymous_internet/Tor_Browser#fingerprint]], Tails provides anonymity by making it difficult to distinguish you from other users of *Tor Browser* (either in Tails or on other operating systems).
So, the information retrieved by such fingerprinting websites is not harmful for anonymity in itself, as long as it is the same for all users of *Tor Browser*.
This second synchronization is made by sending HTTPS queries through Tor to several websites and deducing a correct time from their answers. You can see the list of websites that Tails can connect to in *[[!tails_gitweb config/chroot_local-includes/etc/default/htpdate.pools desc="/etc/default/htpdate.pools"]]*.