before the last battle. free moiraine, get the boys together, battle at the Black tower, Elayne's birth, deal with the seanchan, which happens the same time the boys get together, maybe. I think all that is doable in one book, leaving the last book for the whole of tarmon gaidon. There are also some stuff that could happen but aren't necessary, Mat's final showdown with the Gholam, Fain popping up to wreck something... But still, one book should do it.