Not long, 4 series max probably.
Personally I'd love to see Relf and the defense have a nice half, be up 24-3 at half and then let Russell/Favre play the 2nd half.
Russell looked more decisive against Memphis but looked scared vs LSU (and probably rightfully so). Favre couldn't get a good feel, but on the sack if they guy deep was double covered at least he didn't force it. But he didn't get enough snaps to really make read on him.