Number of cut off days default is 3 if you didn't mention anything in the field.
What number of cut off days will do?\
When a customer has an upcoming charge, the cut off days act as a safeguard. If the customer tries to change their next billing date, the system checks if the difference between today's date and the next billing date is less than the number of cut off days you've set. If it is, the change will not be allowed.\
On the other hand, if the difference between today's date and the next billing date is greater than the number of cut off days you've defined, any changes made will only apply to future billing cycles, providing a clear and predictable billing schedule for both you and your customers.