You won't be able to see the times available until your booking window opens or even if a particular excursion is available for your sailing. I always have a first, second and third choice ready just in case it turns out that, when I book, it either doesn't fit my schedule, is full or isn't running on my sailing. I've had it happen sometimes that the one I want isn't available at all on my cruise and had to pick selection #2 (although some of those selections have turned out to be absolutely stellar choices and, given the option, I would do them again as selection #1). So my suggestion is to be prepared with multiple choices. Also, check back often in case you have to pick #2 and would still like #1. That's also happened as people constantly change plans.