I have used Z2 and Z5 without ZFX. It takes longer to dry without ZFX. They say ZFX "vastly improves paint surface appearance and increases polish durability." ...but I've barely noticed any shine or durability difference using it.
ive done Z2 with about 1/3 the recommended amount in warm (70 degree weather) and it still dried by the time i finsihed applying it. maybe about 15 minutes of extra time i left to make sure, but in warm weather it worked fine.
Shouldn't be a problem... I did a Z2 application last summer without ZFX (oops! just forgot until I was halfway through ) and it dried quick enough for me not to have to wait for anything -- I think I was doing about a quarter panel at a time. I only add a few drops of ZFX anyway.
Just one more of the benefits of high-dry-n-hot New Mexico! 8)