I'm thinking February 24th for CTM, the week after Ripper Street finishes. Two costume dramas on Sunday night may be too much for BBC1 even two costume dramas as wildly different in content and style as CTM and RS.
Also, IIRC, last winter Waterloo Road didn't return until close to end of Midwife's run - BBC1 spreading out their very limited pre-watershed drama. And next year WR starts on 2nd January suggesting Midwife will have to wait.
I wonder if Waterloo Road can improve on it's previous performance. Still it did better than YA in it's slot.