Once you have given your employer notice of the date you intend to start your leave on, you are entitled to vary that date, provided you give your employer 28 days' notice of the new date.
If it is not possible to give 28 days' notice, you must give this notice as soon as is “reasonably practicable”.
If the child has not been placed in your care by this date, then you can choose another date, either pre-determined, or a specific number of days after the child is placed with you, for the leave to begin on. If you are unable to give 28 days' notice in this case, then you must give notice as soon as is reasonably practicable.
Your paternity leave period will begin on the date you specified in the final notice you gave your employer. If you have stated that your leave period should begin on the date that the child is placed in your care, and you are at work on that date, then your paternity leave period will begin the next day.
Once the adopted child has been placed in your care, you must give your employer notice (as soon as is reasonably practicable) of the date that the placement happened.