Firstly, why have 2 back to back, then have 3 days cooldown for TB? Spread the TW out a bit.
Secondly, why not combine the preview phase with the set defense phase? To set defense, one must "sign in" at the same time. Would take a 3 day event and narrow it down to 2. By now we should have our defense strategies on point, and there is no point to give us time to plan, unless we know what guild we are going up against before.