What part of speech is "that" in each of the following sentences that mean the same?

It was all planned well before today that I can be sure about.

Here I believe that that is subordinating conjunction.

It was all planned well before today; I can be sure about that.

Here I believe that that is pronoun, hence the need for the semicolon to separate the two coordinating clauses.

And are they both right? Please correct me if I am wrong.