I would think that ideally, at least the first three months should be available to any woman with a small baby, preferably the first four. I had three months, and after that I could take on hour off for nursing. My baby only needed one bottle in between, so expressing was not a hugue issue, that was for her lunch. Because our working hours in Spain have a 2 hour interval for lunch and it was possible for me to rush home for lunch at 14.00, I had a bit more than an hour with her and nursed her at the end of the period. Her lunch was then 12.00. When she started taking solids (she loved them), at 6 months, I substituted that bottle by a cereal even though that was not what they had told me to do (first breakfast, they said, I think it does not really matter). Then I substituted afternoon meal, as sometimes it was stressful to get there on time, and when I started breakfast I substituted cereal for pureed protein together with carrots, potatoes or rice, and a green veggie (one at a time, if there,s an allergy you can detect it).
I was the only working mom in my building (eight of us had had children at the same time more or less, and all were girls) and the only one nursing. So I did not really feel like a "bad mother", just took it easy. I think the unspoken message I put across to my daughter was more or less : yes, you can have it all. No need to sacrifice yourself, no need to sacrifice your children, it is compatible.
It was compatible for thousands of years, when women worked in the fields with their nursing baby nearby, or at home (do not forget, spinning and weaving were the textile industry, preserving food the food industry, etc). Only industrialization changed that and generated a difficult challenge for us women. Adapting to the situation, being flexible, was the key for me. It is true that I also felt some relief in getting back my own personal life, and that made me stronger to cope with tantrums, bad nights, etc. But I only felt that when my dd was about a year, certainly not before when it was hard for me to leave her every morning.
Good luck to all of you, it will get easier, believe me.