IMO, Taurus mis-labeled the 24/7 Pro DS, Millennium Pro and Millennium G2 as SA/DA. As Pasquanel said, these pistols in fact are in SA always unless when there is a misfired round, the trigger would switch to DA for the second strike and then the trigger would return to SA once the misfired round is cleared. On the 24/7 Pro DS/Pro C DS pistols, you can decock the gun to make the 1st shot DA thanks to the decocker safety.
On the other hand, the 24/7 G2 pistols are true DA/SA, 1st shot DA then the rest will be in SA unless there is a misfired round, the trigger would switch to DA for the 2nd strike and after the misfired round is cleared, the trigger would switch back to SA.
Edit: The 24/7 Pro/Pro C DS and 24/7 G2 guns have the cocking indicator to help us easily tell when the trigger is in SA and when it's in DA. On the Millennium guns, because they don't have the cocking indicator, we have to feel the long trigger pull of the DA trigger.