You should be able to manage an hour walk each day (dependant on weather), although it will all depend on how the birth goes and how you go with those first few weeks (I had a csection and was very impressed with myself for walking the 400m to the beach after 2 weeks and that was with DH pushing the pram). You will be tired getting up twice a night (or more) for who knows how long. But particularly when DD was little the walks were great as she would fall asleep in them. We tried to go for one each morning and then if she wouldn't have an afternoon nap do another one then.

Walks are great as you can do them at any time of the day, you're not stressing about her sleeping through the class you want to go to at the gym etc.