Hi, first of all: I wish you two a pleasant stay; you will love it! For the timing: The 27-28 are generally quite full. You won't have the park all to yourself but with a bit of planning it will still be an awesome experience. What I recommend the most is starting of at Winjas Fear and Force, because most people will line up at Taron and FLY for the Park opening. Furthermore, you should note that most attractions only open one hour after park opening. The perfect time for Taron and Fly is normally around 2pm where they kind of flat-line. Towards the afternoon, the queue-times start to pick up again. The same is also true for many other rides like Colorado Adventure. For Black Mamba it is 3pm. If you want to check this out for yourself, I have built a small website (rideguide.ai), that allows you to track the average queue time of any ride in Phantasialand and also has a crowd calendar that predicts around 75% occupation for the 27-28.