It needs a minimum of 3 days to topcoat depending on air temperature, humidity, and whether or not you used an accelerator, and yes, it needs to be sanded.

Dont know

You have to hit it real fast with an orbital and 360 to ruff it up or the base re-coat will not come out smooth and stick right. The base wants a porous surface to cling to, it will bead like water on wax if you shot it on clear coat.

dont know

i painted a bumper with ppg basecoat paint and cleared it with ppg 2042 clear. the color is dark, so i was going to repaint the bumper, can i paint over the new clear being it has been less than 24 hours, or will it need to be sanded first?