I would not worry at all. Every person is different, therefore every surgery experience is different even with the same surgeon.
I was told I'd be in the hospital up to four days and I was released in two days. Some in this forum were released in 24 hours.
Your dad's body is just reacting a little differently and I'm sure your health care professionals are doing what they believe is best for him.
Don't worry about
when the drain is coming out. That is different for each person as well.
Try to stay calm and give him all the encouragement you can. I would stay on top of what is going on in the hospital. Ensure that he has everything he needs and that you're paying for!
I wanted to drink a lot of fluids and I had to keep on top of them to have enough ice water and juices.
Your dad should do just fine.
We're sending our thoughts and prayers out to you and your dad, Julie!
All the best,