Thought about this earlier. Last season none of the summer signings played a single pre season game and yet they came into the team first game of the season and were brilliant... fitted like a glove. So whilst the earlier the better, it makes little or no difference I dont think. Just get the best price and make the money stretch as far as it can go.
They all got long injuries at some point throughout the season, which could have been down to not having a full pre-season.