My shortest turnaround time is 20 minutes, my longest turnaround was 6 and 1/2 days.
An MD admissions officer
and a well-known pre-health advisor at my school both recommended turning in secondaries within 2 weeks.
@phunky, apparently there are adcoms who say exactly that. Maybe not after 16 days, but if you wait nearly a month to turn in a secondary, then they might look down on that. I'm not saying its true for all schools, or even most of them. But I know for a fact that there are some adcoms who stick to the unspoken < 2 week rule.