That seems to be correct. See the bottom of the Noggin schedule page (
N O G G I N: TV Schedule) to find this information:
"At 6pm ET every day The N, the teen block on Noggin, takes over the channel."
More proof comes from the Noggin FAQ page (
N O G G I N: For Parents: Frequently Asked Questions):
"WHAT IS THE N?
The N, a Nick Digital Television network aimed at teens, succeeds NOGGIN each night. The N's teen-centric programming airs from 6pm-6am (ET) nightly. The N's award-winning comedies, dramas and reality series feature older teens and tackle the tough issues that many teens face. While these programs are entertaining and thought-provoking, they contain material that many parents may not find suitable for younger children."