Trusted time data is time data from a provable source. Because of how time is moved through networks over the Network Time Protocol time sources should generallty only be used which are local to the user no matter how good the network performance is. This is because of how peering agreements and routing based therein is accomplished and the uncertainty it presents.
In many jurisdictions there is a legal basis for who is the keeper of that jurisdiction's trusted time source, and in any instance where legal culpability is required time should only be taken from those sources or commercial providers who can fully isolate the relying party from any 'pain' they might encounter for using that official public source of time.
For those parties a commercial source of time who abstracts the end-user from culpability under the Freedom of Information Act FOIA in the US and other legislation in other countries, provides the best source of time data.