Depends how fast the pump is running at the smallest size? If, in the time it takes to build the settler, an extra citizen could produce enough food to pay for himself (i.e. 10) then it is no problem for him to be there. If he produces less than 2 food, then he is wasting your time, and if he is producing more, he should be speeding the process up to some degree.
But I don't think settler pumps take much planning, compared to Civ3 at least. Because of food and shield over-runs being put towards the next build, you can't go far wrong with just building a stream of settlers as fast as possible. Making sure to always pop the settler with <10 food until the next growth (so that the town instantly grows back after the settler is built) might earn you an extra couple of food / hammers in the cycle, but it isn't major.