Z5 wasn't available when I used the Zaino line but from my understanding from the Atuotopia posts, Z5 is an un-polish in that it has no abbrasives, just fillers to hide swirls. If that's true then you can use it as often as you like/need.
p.s.
These gloves or similar are good to keep in the car when you quick detail your wheels, tires and glass. Doing just those two things makes the car look just washed....without having to touch the paint. Chemical Guys make great no frills products. I'm about to order some of their towels to test them out.
http://www.chemicalguys.com/Detailing_Gloves_p/acs_999_2.htm