As it is in a pot it can go straight into the ground now.

Remember to make the hole at least 2x bigger than the pot it is in. mix the soil with some compost so when you plant it and back fill the roots have plenty of good soil to grow into. keep it well watered for several months, even if you have some rain.

Happy Birthday!
You're spoilt for choice really. It's more a question of where you want it to grow & how you want to prune & shape it. Learning a bit about pruning apples in their first few years to get the most out of them long-term helps avoid disease problems, etc.
Sunset can be grown in a container so waiting for Winter dormancy wouldn't be a problem. If you put it in the ground the couple of weeks after complete leaf drop would be ideal, before the soil temperature drops more & when there's regular rain.
If you plant it in the ground, make sure the hole is twice the size of the pot & holding the trunk as low down as possible give it a good shake to tease out any bound roots from being in a pot

https://www.gardenfocused.co.uk/fruitarticles/apples/variety-sunset.php

Thank you for your good advice, I would be lost without all the great help GYO gardeners have given me.
Looking forward to some lovely apples in the future.
Thanks Cecelia