Couples recommends on the Romance Rewards tab doing pre-checkin a minimum of 3 days prior to your arrival. This gives them time to have your perks ready. We have done this on our last few trips, and have never had a problem with receiving massage certificates, invitations to the repeaters dinner, etc. In fact, I usually pre-register about a month or so ahead of time. It gives me something to look forward to, and I don't have to worry about forgetting to pre-register in the rush the few days before vacation. Just be sure to check your flight information, and to let them know if anything changes prior to arrival.
And, yes, you pre-register under the Romance Rewards tab at left.
Yes, u can register and do pre-check in for your first trip. My co-worker went one her very first trip to CTI in 03/2010 and she came back to work, we went on her account to see if she had gotten credit for her trip and she did. I think u should register for your very first trip because, that's how the points add up. IMO, it's a 50/50 chance of them posting your points and getting u your perks, whether u pre-register online or not. It's the luck of the draw.