I've asked clinician-scientists this question, and the overriding principle is that you want to give the medicine time to work. My old routine was to do albuterol, pulmozyme, hypertonic saline, and then tobi (if I was on it), but I was told that by doing hte hypertonic saline immediately after the pulmozyme, I was basically washing out the pulmozyme.
I seem to recall that Pulmozyme ideally needs about 20-30min to work, and the effect is usually gone by 2-4h, depending on a number of factors. So, I personally think it's a good idea to sit tight and avoid exercise or hyper-sal for 30min after a dose, after which you can give hyper-sal or start playing/being active.
Considering all these things, I personally do my pulmozyme at night, just b/f bed. But, if one is pressed for time, Pulmozyme at any time is better than no Pulmozyme.
Hope this helps!
edit: Note: "active" above ("playing/being active") means vigorous physical activity...walking around the house or into school shouldn't affect the medicine's ability to work b/c those things don't often make you cough more than usual. you're not clearing the medicine out by doing these things.