It is important to decide in advance what the absolute cutoff conditions
are for making the system update work. The cutoff has to give sufficient
time for the back-out plan to be implemented before the service must be up
and running again. The time by which the service must be up again may be
based on a committment to customers, a business need or may be because
this change is part of a larger sequence of changes that will all be impacted if
this service is not restored on time.