If the leader said to inform the customer before 15, then you should inform the customer at 15. It is a necessary process for childhood customers to communicate with leaders before communicating with customers. If the leader says that the work progress has changed at this time, then you must communicate with the customer according to the leader's requirements.
It is very normal that the schedule is almost inconsistent with the schedule, which is related to many factors. After all, there are too many inevitable external factors. Therefore, the work can be carried out according to the notice and arrangement of the leaders. Don't make your own decisions, let alone complain. No job is easy. What we can do is to do our job well, make no mistakes, and then solve the problem according to the requirements of the leaders.