During the build
If a change is required for the original job (a payment provider that will not certify, a store rejection), we absorb or we re-quote in the open. If it is a new job, it waits or it is paid.
After launch
The 30 or 45 day window is for defects in the original scope. New features are a retainer or a new package.
Fragen
What if we disagree?
Work on the contested item stops until the change is signed. The rest of the original scope continues.