I stopped expressing when DD was 6 m as my spare Milk was non existant! Before that I would express some Mornings using an AVENT hand pump. Early on I could get 6oz in about 10mins but this slowed over the months to about 2oz after 30mins - that is when I gave up.
I think if you do it every day at the same time you would be able to build up a good routine, a friend of mine did this as she returned to work pt very early. She expressed every morning and evening and she had enough for all the feeds while she was out. Can't tell you volumes but she did say she had loads of Milk all the time and her norks were huge