It's been so long ago since I used Z1 that I can't remember much about it, but if I recall it functioned the same as 601 in that you put a coat on, leave it and then add Z2, Z5 etc
601 can be used that way, but I prefer mixing it 1 to 4 (.5 oz 601 to 2 oz 105) with 105 (or 111), apply a thin layer, let haze and buff off. Couldn't be any easier. It allows you to then top the 105 with whatever you want in a couple of hours rather than waiting overnight. I have 105 topped with POXY on my Passat and it has never looked so good.