Bleaching seems a simple process but if the right elements are not all in play you don't always get the desired effect. If it is windy, you get drift you don't plan on, if it is cloudy or cool it wont bleach clear white. These are things to keep in mind when requesting a bleached shirt. Bleaching can potentially cause a delay in shipping.
This photo explains the difference in cloudy and sunny days. Bleaching is best done in the summer. While it can sometimes be done in the winter you won't get the same results.