It took weeks, maybe months for Impact's audience to adjust to the new timeslot, while WWE's audience was adjusted after, what 3 weeks, if not earlier? Of course the event of RAW 1000 probably helped A LOT.
I agree that they should've stayed in the same timeslot, but I also get why Impact was the lead-in for MMA Uncensored. It worked with UFC and that show is Spike's show, so they probably wanted the best ratings possible, while counting on Impact's audience to properly adjust to the new timeslot. If that show would have been the lead-in for Impact who knows if that show would still exist. But back to Impact, you can't check if your angle's are catching on to the audience, if the audience still has to adjust to the new timeslot, so your basically just treading water. They should've done 1 thing at a time, instead of changing time slot and going live all at once.