If you track your cycles, I would suggest starting to drink the tea the day or two before you anticipate your monthly dip in supply. (exclusivepumping.com)
dip in supply when they return to work — don't panic! (tinyhood.com)
So let's say your supply is doing fine, but then takes a dip due to one or more of life's happenings, such as your baby starting solids; a decrease in the number of daily feedings; night weaning; a return to work; recovery from an illness; or dips in supply due to medication use, such as antihistamines or birth control pills. (getboobiebars.com)