Um, most tournaments run a couple of hours. I got into the quarter finals of a tournament with like 100 people. It started at 6 PST, was over by 8:30, I was done by 7:15. That isn't what I think of as a major time commitment. If I have like a thousand people sign up, sure, maybe play it out over a couple of days, but I don't think that is very likely. Apparently you don't either, since there are "few enough of us."
What you are thinking of is called a sideboard. Until it is implemented in the client, I think sideboards in HS are simply not a practical idea for tournaments. MLGs tournaments you can change your whole deck, though not your hero, between matches, win or lose. That is a bit silly. With TL's format, which it should be noted is the format used for basically all major HS tournaments except MLG, if you lose, you get a whole new deck, because you're playing a different hero. If you win, you're "stuck" with the deck that won.
Sorry you can't predict availability. I'll arrange it so sign ups are, at a minimum, up to the day before so if you happen to be available you can participate.