Let the date come from someone other than you
Reposting is instant and denial is cheap. What is not cheap is a timestamp that existed before the argument did.
You seal it the day you make it
Before publishing, ideally. Evidence created after a dispute starts is worth far less than evidence that predates it.
You get the certificate
A PDF carrying a thumbnail of your work, its SHA-256 fingerprint, the exact hour and a QR code.
Someone disputes it
You send the public link. They check it themselves, with no account and without going through us.
It holds up on its own
The RFC 3161 seal comes from an external time authority and the anchor is in Bitcoin. Neither depends on this company still existing.
Being straight about the limit
This proves the file existed at that moment and has not changed since. It does not prove you authored it — anyone can timestamp a file they did not make. What it gives you is priority, and in practice priority is what most of these disputes turn on.