Hello from your fellow cruiser!!
When I cruised with DD who was 6 months old at the time, I found that she had a complete melt down at dinner. She was used to being in her house at 5 and liked to be in bed around 6:30. I had visions of family dinners but DD was just so miserable. I ended up putting her in Flounders every evening at around 7 so I could enjoy the shows with DH and DS. We then picked her up at 9:30. I had pre-booked a few evenings ahead of time, but after the first night, I went in and booked her for every evening with no probs. However, towards the middle/end of the cruise, I noticed lots of people at the Flounders desk trying to get time and it wasn't available. This was a January cruise about the same time as we are sailing this year.
My latest DS will be 10 months on the cruise. I booked him for every show night from 7:30 until 10 and on Pirate night until 11. He is much more of a night owl so I am taking him to the show the first night to see how he does. We may modify after we get on board - you can always cancel with 4 hours notice??? I know I do NOT want to carry him through the entire Pirate show so that is non-negotiable. I also scheduled an hour or so the first sea day in the afternoon so that he can get used to it. That way if he is asleep when I drop him off the first evening and wakes up, it won't be a completely strange environment
I would look at your child's routine/temperment. If he hates noise/chaos and is used to early bed time consider booking during the shows after dinner (if you are main seating) or during dinner if you are late seating. If you have lots of hands to help hold him, you might not mind keeping him during shows/pirate night (assuming he will sit quietly). If you have already lugged him around all day, or chased your crawler, you might want a break and Flounders will put him in his PJs, give him a bottle, and put him to sleep in the crib while you enjoy your evenings!!
I am using a vacation week at daycare so figured the money I would normally spend at his daycare I can use towards Flounders so I pre-booked just about every evening.
I don't think you can just show up and expect a spot!!! If they don't have enough kids booked, they probably give the staff time off or move to another location so they might not have the staff to accomodate and maintain ratios.