as far as I know they have at least three different render node setups, so some of them will render slower, and they also differ in terms of the RAM available
also different buckets/parts will obviously take different amounts of time depending on what is in the individual buffers and it's complexity, ie an extreme example would one node rendering just sky but other a full car with motion blur; the difference will be 100x. a node taking twice the amount of time than others is somewhat within range unfortunately, if it was more I'd perhaps be concerned