Well I had to think of a time to run it, and 30 min just popped into my head, this was 2 years ago now I think, been a while since I first made cleanmem. I just always kept it there.
You can change the value in the windows task scheduler. I say change it to what fits you needs. For example, I am on a system with 4gb of ram, my memory never gets completely used up. So the 30 min is perfect to help keep things smooth.
Now lets take a person with only 1gb of ram and they are using some memory hungry apps like Auto cad. Well their memory keeps getting eaten up every 15 min or so, so setting cleanmem to 10 min keeps their system running smooth.
So a good rule of thumb is how fast does the memory get eaten? How fast does a memory leak in a program climb? (Like multimedia in Firefox)
Then adjust the time cleanmem runs to that

Shane