I like your suggestion of using Punk at the top of one of the hours on his own to check out how he does, but the 9:00pm timeslot is going to receive the asterisk that the Bryan/Sheamus streetfight did this week, as doubtless a healthy number of viewers forgetting about the first hour are just showing up to join the viewers who were along for the ride in the first hour. At least for a good while, anyway.
Pretty much this. 8PM is no good right now because not everyone is tuning in at that time yet. 9PM will get the big gain for the next several weeks as mentioned, and the 11pm/overrun, even if Punk was in a segment by himself and gained 1,000,000 viewers, it would just be because "people were tuning in for the next show".
The 10PM slot is the only place Punk can do no wrong if he gained big, but that slot doesn't gain like it used to (besides when there are 2-3 huge names in it like Taker/HBK/HHH earlier this year).
Also for this week, in addition to what I said already, I'm sure Punk's commentary also kept people from tuning out and bringing the overall gain up due to people wondered "What would Punk do?" Personally I was hoping he'd drop another big "pipebomb" like last year. He kinda did it with Lawler but I was hoping for something a little more hard-hitting by the end. Oh well, perhaps we'll get something in the next month or so.
Also hopefully Punk calls Rock "Dwayne" a lot more in the future. The reaction on here for it in the Raw thread was hilarious.
(And I don't normally like the whole "calling them by their real name if they have a character name" thing, but people's reactions were beyond hilarious).