In NYC, it aired at 1 pm on WNBC Channel 4 Mon - Fri. I think it stayed there for its entire five year run. WCBS Channel 2 was airing WML with Larry Blyden at that time.
In New York, it moved to WOR/9 sometime along the way, 1976? I could also watch it daily from WTNH, New Haven, but they were always a full season behind. Last on the cycle.
Channel 9, 6pm. Part of a game show block that included Joker's Wild and Bowling for Dollars. I remember it well! 
From memory:
The WOR game show block started around January 1, 1977 with reruns of the latter-day CBS
Joker's Wild and original episodes of the Larry Kenney-hosted
Bowling for Dollars. (New York Mets broadcaster Bob Murphy had hosted a previous run of the show for a short time a few years before.) By the fall of 1977, the block was expanded to two hours, and included first-run syndicated episodes of
The Joker's Wild,
Bowling for Dollars,
The Hollywood Connection, and
Concentration.
Concentration had been in the 1 PM time slot on WNBC for several years (before that,
It's Your Bet had run there, and I'm guessing before that it was
PDQ). NBC and CBS didn't program anything in the 1 PM slot for a very long time. WNBC ran
Somerset at 4 PM for several years, followed by a 90-minute movie and then local news. Sometime in 1974, WNBC expanded their local newscast to two hours, from 5 to 7 PM (which wasn't a bad idea; the competition was Mike Douglas on WCBS, another movie on WABC, and kid-oriented programming on the three independent stations). My memory is
Somerset stayed put and WNBC programmed several different shows in the 4:30 time slot (
Room 222 reruns for awhile, and then
The Diamond Head Game). In the fall of 1975 WNBC switched to
Marcus Welby, MD reruns (under the title
Robert Young, Family Doctor, since it was still in first run on ABC) from 4 to 5--my guess is
Somerset moved to 1 PM and Concentration probably got bumped back to 9:30 AM for the next year or more. (I don't remember when Phil Donahue took over the 9 to 10 AM time slot.) If somebody has a good New York metropolitan area
TV Guide collection, they can adjust or verify this.
And yet I can't remember where I left my car keys just now.
