org-deadline-warning-days

org-deadline-warning-days is a variable defined in `org.el'.
Its value is

14

Documentation:
Number of days before expiration during which a deadline becomes active.
This variable governs the display in sparse trees and in the agenda.
When 0 or negative, it means use this number (the absolute value of it)
even if a deadline has a different individual lead time specified.

Custom commands can set this variable in the options section.

You can customize this variable.