At worst you'd lose the money that the seeds cost. But if it succeeds you'll have a jump on the next season.
I put seed down two weeks ago and ended up with a few bare spots (mice, washout, birds, who knows) and so I put down a little more yesterday.
Who knows, we may end up with some nice weather before things turn ugly :) With all this rain we've been getting, my new grass seems to be doing very well so far. If any of the late seeds come up, bonus :)