I'm not a lawyer, but timing-wise the grand jury first needs to finish and then vote to indict TFG before he can be arrested. The indictment probably won't happen until later in the week. TFG will likely have the opportunity to announce it before anyone else because the DA won't publicly disclose until the arrest happens.
"Prosecutors working for Mr. Bragg have signaled that an indictment of Mr. Trump could be imminent. But they have not told Mr. Trump’s lawyers when the charges — expected to stem from a 2016 hush money payment to a porn star — would be sought or an arrest made, people with knowledge of the matter said. At least one more witness is expected to testify in front of the grand jury, which could delay an indictment, the people said.
One of the people said that even if the grand jury were to vote to indict the former president on Monday, a Tuesday surrender was unlikely, given the need to arrange timing, travel and other logistics.
The statement from Mr. Trump’s spokesman did not explain how he had landed on Tuesday as an arrest date. One person with knowledge of the matter said that Mr. Trump’s advisers had guessed that it could happen around then, and that someone might have relayed that to the former president."