What does 7c mean in this poster?

No. The "P" means "8 P.M." (evening) Eastern Time (implied) and "7 p.m. Central". The P does NOT mean Pacific time. 8 p.m. Pacific time is 11 p.m. on the East coast.

A live broadcast (or taped show that goes out on air) at 8 p.m. Eastern Time would be seen at 7 p.m. if you lived in Central time zone. That's why it is advertised this way, presumably somewhere on the East coast of the U.S.

"P" is a trendy abbreviation for P.M.

Actually, in this promo poster, the 8P 7C means: Broadcasts 8:00pm (Eastern time by default), 7:00pm Central Time (since Central Time is an hour behind Eastern). P = p.m., C = Central Time.

Looking at the POP schedule page, one can see that they use P to mean PM. And on the homepage right now there's an ad for the show saying it's on at "8/7C". Hmmm, they left out the P completely?! (Maybe they saw this question.)

More revealing is a look at a news item for the season premiere in question, which says,

Small town living continues for the Rose family in the season two premiere of SCHITT'S CREEK on Pop today, March 16, 2016 at 8:00 PM, ET/PT

-- meaning, the show is at 8 PM both in the Eastern Time and Pacific Time zones. (From growing up in ET, I know that networks tend to combine the ET/CT areas. So, 7 PM Central Time fits also.)

Conclusion: Everyone is right! P means both PM and Pacific Time and C means Central Time.

(Whew, glad we figured that out. Now, has anyone noticed the casual way the guy's holding his jumper cables? Could end up with a thumb welded to a clamp, or something...)