With Saturday Night Live airing way past bedtime for most of Justin Bieber constituency, the NBC late-night sketch show did not get a boost from the young pop star’s stint as host and musical guest last night. SNL averaged a 4.9/12 in the metered-market households, down 4% from the show’s most recent original hosted by Adam Levine.  In the 25 markets with Local People Meters, last night’s Saturday Night Live drew a 2.7/12 share in adults 18-49, also down 4%.