The kind of exchanges I've taken part in are small and relaxed and there's usually a calendar for posting where each author gets a certain date. I always have to ask the mods to move my date down and down and, well, I've been known to post after the exchange had finished more than once. That's why I try not to take part, because I suck at deadlines and it's more work for the mods, who are already investing a lot of their time in holding the event (I admire greatly your genetical disposition to fulfill them but, alas, it seems to be the other way around for me).