My daughter was 18 months old when I started PT school. I'll be graduating in May. There is one person in my class besides me who has kids. He has three, and his wife is a stay-at-home Mom. These are the things you have to watch out for:
1. Our families are in Washington state, Colorado, and Montana. I'm doing PT school in North Carolina, approximately two days drive from our nearest family member. Our daughter has spent time with her grandparents maybe 4 times, and to be honest that really sucks. She's young enough that she doesn't remember them between meetings, so they remain strangers. They have to start over every time they see her.
2. Hopefully this won't be a problem for you since your fiance works in daycare, but we're lucky my wife's work has been understanding. When you are in this program, it is a job, and it takes priority over every other engagement in your life. My school will expel someone for missing class too often or even being late too often, just like a job would. If they spring something on you, and you or your fiance have another obligation, that's just too bad. For a person without kids, this isn't as big a deal, but for people with them who have no one to watch the kids last minute, it means cancelling what you had planned. There have been multiple occasions that I got an email on Thursday saying a professor had decided to do a makeup class on Friday because we were behind. That means that if my wife was scheduled to work, she had to call in or try to get her shift moved, because we have no babysitter or other child care. She has been written up at work due to too many absences, absences that were directly related to the fact that she had to stay home to watch our little girl when a last minute school engagement was sprung on me. The same thing would happen in the case of something fun that either of us had planned. Be prepared for that.
3. You need to have a serious conversation with your fiance about what's going to happen when this little one comes along. PT school is no picnic. In my school, if you get more than two Cs, you're kicked out. You'll have to spend hours upon hours studying to make these grades if your program is worth anything. When both parents are home, people are used to thinking of child care as being a 50/50 deal from Mom/Dad, but when you're in PT school, that will NOT be feasible. You'll be able to help, but not as much as the typical father. Is she prepared to take on most child-rearing responsibility even when you're at home without keeping score or resenting that you don't have as much time as you wish you did to help her?
I guess the bottom line is your external support system isn't nearly as crucial as your internal one. The attitude and flexibility of a PT student's husband/wife is what really makes or breaks whether or not parenthood is joyful or miserable for them during PT school.