We have travelled with OV four times now and each time we were on an early evening flight. Technically this gives you a bonus day on the boat or in Palma but there are a few drawbacks. Firstly you have to be out of your cabin by 8.30am in order to allow the staff to prepare for the new lot coming in. Your main luggage has been taken away but you still have your hand luggage with you. This can be left in the Marquee (at your own risk) but otherwise you have to lug it around wherever you go. We have left stuff in the Marquee (obviously keeping tickets, passports etc with us) and it came to no harm but, you never know, do you? You can hire a cabin for the day (think it was about £40) if private facilities/bed etc are important, otherwise you just sunbathe/swim/read etc as you see fit.
On OV1 there is a cinema which is air conditioned and very comfortable and that helps to while away a couple of hours. On OV2 you can have a day pass to the Spa section (£10)which has wonderful relaxation zones.
Change over day is always a bit frantic as by mid-morning you have a lot of the new people arriving (not knowing where anything is) and most of the "seasoned" travellers waiting to go home. Each time we found that the older passengers liked to sit by the exit doors in the Reception area and just wait - even if their flight wasn't for many hours.
An important thing to note is that the card that you use to charge all purchases ceases to be valid from about 2am on the day of departure. From then on, any purchases have to be paid for in cash (sterling). If you are on a late flight you are going to need lots of drinks during the day, so keep some sterling handy.
Hope this helps. Enjoy your cruise.
You will be checked in by OV and only taken to the airport at the appropriate time. On our return in May, our flight was delayed but we were able to stay on the ship with comfort and food until close to the changed time.