Amy Poehler's baby boy arrived over the weekend with impeccable timing -- on Saturday night, natch. Poehler's "Weekend Update" co-anchor, Seth Meyers, announced the birth on Saturday Night Live: "Amy Poehler is not here tonight, because she's having a baby."Archie Arnett was born to Poehler and her husband, comedian Will Arnett. On Saturday's SNL, former castmate Maya Rudolph and Kenan Thompson serenaded Poehler (via television), singing a duet with customized lyrics to the tune of Frankie Valli's "Can't Take Eyes Off Of You."Rudolph, meantime, returned to SNL for a guest appearance as Michelle Obama. She had reportedly planned to reprise her "Bronx Beat" skit with Poehler as well, but was thwarted by baby.