HUMS Download frequency
A question for you is "What do you want HUMS to be able to tell you? That a part of the aircraft is developing a fault or a part of the aircraft failed at a particular time because it wasn't diagnosed early enough!"
Also, it's not the data downloading that's so important but what you do with the data afterwards and how quickly.
Data collected and reviewed after every flight will significantly reduce the probability that a failure will occur during flight. Data collected weekly and reviewed whenever will only give you a cursory overview of what is happening to the monitored items.