Changing Time Machine backup time

Just got my external WD My Book 750GB HDD - it's a beast! However, when running it is quite noisy (at least, I would say, noisy enough to keep me from sleeping). Time Machine does a backup, as you know, every hour. This causes it to awake from spin down (which is silent) which then turns noisy.

Is there any way to either:
a. Make the WD drive take shorter than 10 minutes to spin down?
b. Make backups when I want (e.g. 8am - 10pm).

I have found that I can edit a config file which contains the second itervals which backups run. I have also found TimeMachineEditor which provides a GUI to do this.

What do you all think, is it safe to go changing the config files...?