On the Wonder, last time we sailed, there was a couple's villa at 8:00 AM that we took. It was a great way to wake up and start the day with a spa treatment, which included a soak in the hot tub, fresh fruit, tea, time on the spa verandah snuggled up in a big fluffy comforter in the cool morning sea breezes while we did so. Due to the other events we wanted to attend, we wanted to take the earliest appointment. I think we may have had a brunch at Palo that same day at around 11:30, so it was perfect. Fabulous way to start the day. Don't wait to book your spa treatments until you board - do it online as soon as your booking window opens. The couple's treatments go pretty fast, and there may be nothing left at the time you board. Even the days they have morning treatments open may book quickly. You have a lot of time to change your mind and switch things around after you book online.
In the past, we've also booked the couple's villa after lunch and before our early dinner seating. That is nice, too - but make sure to leave yourself plenty of time to shower and change for dinner. The couple's experience is about 2 1/2 or 3 hours. Possibly closer to 2 hours?? My memory is a little hazy on that, although 3 hours rings a bell.