In AE you can bump deliveries to a later date (for free), but you can't make them faster if you chose to have less than max frequency... And now I've had another situation where I thought I won't need so many planes so quickly and I'm having a bit of a shortage and regret the decision to put the lesser frequency...
Also, there might be some financial incentive from the producer to have more or less deliveries, especially if we bring in the system depending on how busy the producer is, something along the lines of what dazwalsh wrote.