As far as I can tell, the only deadline is to have your block finished and posted to her linky party (or emailed to her) the day before the next block is supposed to be revealed. That gets you the next block free. Personally, I would have it in a couple of days early. That's just me.
If you miss the deadline you can buy her next block and get back on track.
You can do the block, or placemat or game.
Have you received your first block yet SewExtremeSeams?