From my own experience, this is how things went for me. For the few months, they sleep, a lot. So you might get out a few times more than what you might think during that first 6 months. Then, they seem to come alive, start to see you, find their hands, take a few steps and believe me your not going to want to go fishing much with all that magic going on.
After they are a year old, the afternoon naps are probably gone, and things get busier. Your going to wish they sure would start to talk more. (You may regret this wish in the years to come)
You may get out fishing less, but your life will be full. Enjoy these times, the years will pass as a blur and before you know it they will be 10. Then, your worst fears could be realised later when they are teens...they may/will come to conclusion that their Dad is in fact not the coolest guy on earth. This, will hurt a bit. It will be true though, so prepare yourself.
My advice, for the early years, keep fly tying, practice your casting, get out when you can. Take lots of pictures of your little one out with you. Get your wife out of the house. Learn everything she does in the house and do it well. (forget the breast feeding part)
You will find time to go, and if you can't go, try to find gold in just staying home.