How many hours did you spend studying the first year material for the entrance exam?
This is probably a late reply, but here is the answer for those needing help in the future. The suggested number of study hours are 10-20, recommended by TU Delft themselves. I doubt there will be much change to this in the future.
From my personal experience, 12-15 hours should be plenty (depending on your study pace). Note that there is quite a lot of new material to cover, but if you truly love the aerospace field, it should be a breeze