Depends on what needs to be done. If you're talking a cheap set that you're just replacing the springs with, then a couple hours. If you're installing GC with custom perches, simple adjustable rear then a couple more to cut off the factory spring perch and weld on new ones.
If you're talking real coilovers front / rear, then factor in about 8 to 10 more hours of race shop fabricating for the rear. But I doubt that's what we're talking about.