Several ways to do this. Maybe Harald of Norway is delayed further, but I don't see why - even a Viking wouldn't want to sail in the winter, would he? I think it's more likely that William gets his wind earlier in the season and lands in the summer or earlier fall. In the summer, Harold of England was encamped with an army on the Isle of Wight, waiting. He disbanded it a little while before Harald of Norway landed; I'm not sure quite when. How much earlier were you thinking?