you should start preparing your milk stock now,but as your BB uses up all milk everyday, why dont you pump as you feed, i found that the milk production increase in this way. I express milk once every 5-6 hours, the one done in the middle of the night may yield 6 oz . Does your BB drink " night milk"? You may pump as you feed in that time as well. I returned to work for 2.5 months now and has been able to maintain 100% BF for my BB and i am trying all sort of method to ensure a good yield of milk production, fish soup, herbal tea, eat more carbohydrates, soya milk, 通草奶, red beans........
good luck to your return to work.