breastfeeding question

I have my monthly check up in a couple weeks but it always happens, they ask if I have questions and I forget everything I've wanted to ask. So with it fresh on my mind.. could I breastfeed only at night? Will my body know to produce milk only at night? I'm going back to work after 6 weeks so I'd like for the sitting to formula feed or use my milk if I pump. This is my first and I really don't even know where to start. If I feed at night will I be leaking during the day? Will I have to pump during the day? Any help please!