Parameter for 'Released Date' / state change date

On our PV watermarks, we want to add the date the CAD document was 'Released', in other words when the object did a state change from 'under review' to 'released'. On out format, we did have 'PTC_WM_MODIFIED_ON' parameter, but the last check-in data can by days away from the released date.

Can anyone point me to the correct parameter?

Thanks, Kathy