Hi,
The delay between two ATD read is necessary as the ATD needs time to complete a conversion.
With simplification, an ATD works by filling different internal capacitors. This requires time to occur.
The time for a conversion to complete is in the datasheet of the product you are using.
There is no absolute answer for all devices family and all resolutions.
In the Electrical Characteristics, ATD Operating Characteristics.
Look for ATD Conversion Period if it is an S12.
Cheers,
Alban.