Again, like Palo reservations, the best times are booked when you get there immediately after boarding. A lot of "slots" are taken up by concierge level guests, so you should have a few times/dates in mind before you get there.
Often there is a special offered for a certain time slot, so be aware of that! Years ago, there was an offer but it was during Sail Away - and my thinking is, if you've been to one sail away, you've been to them all - so I took that special. It was a great way to start the cruise, but I certainly didn't want to go to early dining after being SOSOOOO Relaxed!!!
Rae