Diamond is incredibly chemically stable and inert, which allows us to clean dirt off the surface using dangerously strong chemicals. A three-acid mix is effective at cleaning off the surface.
Before using chemicals, they are obliged to read the safety data sheets. see MSDS material safety data sheet
Raising the temperature does increase the reaction speed, and should make it faster to clean a diamond. However, this effect is non-linear and difficult to predict. When the strong acids are boiled at too high a temperature they can produce highly toxic gases such as NOx.
In short, do not set the temperature above 130 degrees celsius for the heat block and 170 degrees celsius for the sand bath.