Usually that's due to it being too thick, or not dried completely. If it's streaking, it needs to dry longer. If the coat that's put on is too thick, it can take *much* longer to dry. Go for as thin a coat as you can.
Something that helps a lot is the accelerator that Zaino sells. You put a few drops of the stuff in a small bottle with Zaino z2 or z5 and it speeds the drying time up dramatically.
The only other thing that I could think of is maybe you were using z6? If so, that one isn't supposed to sit at all. Spray on and then immediately wipe off.