How can someone combine a timestamp server with their own personal signature?

I found this online:
https://tsa.safecreative.org/

Then perhaps I create a work of music. I want to timestamp the creation of the music by combining a time stamp hash by 3rd party authority (as above) with my own public and personal key.

I illustrate as such:

hash(music work) + hash (timestamp) + hash (author key) = new hash of copyright proof of date/time creation

the important aspect here is the timestamp service has to be 3rd party.


Is such  thing possible? How to combine it with bitcoin or other coin? Or maybe entirely free (piggy backing on blockchain transaction times)