What is the expected delay on a dali ballast from actioning a Direct Arc Power command
The specification requires the command to be handled immediately after the stop condition which is 2.4ms from the last edge of the message. We can see this from the requirement to measure the fade time from the stop condition that triggers it.

Part 102 is Control Gear - This is the IEC term for equipment that is connected directly to lamps, commonly called ballasts or drivers. Part 103 is Control Devices - These are such items as controllers which send message to gear to change their state and level. There is very little commonality between 102 and 103 because the common requirements are now gathered in the expanded part 101.