Mine were in for 180 miles, the dealer didn't know they were in there, no wonder it rode so rough on the first test drive..
I know guys in my Corvette club that left the mag ride spacers in for YEARS! They were never removed during PDI and some of those guys didn't know any better. All I know is that all said that the ride was noticeably better when they were removed! Uh, yeah, you think?!