You will find that some plastic surgeons do, some don't, use drains with breast reduction surgery. In my practice, when I do use drains, I remove them when the output is low (this is usually possible 3 to 5 days after surgery). I hope this, and the attached link, helps.
Like many of the other responders, I do not use drains for breast reductions. However, when I use drains on other procedures they are removed based on drain output, not on time.