The trade union representative shall inform his employer of his absence for the training provided for in article L. 1453-7 by any means giving a date certain:
1° At least thirty days in advance, if the duration of the absence is equal to or greater than three consecutive working days;
2° At least fifteen days in advance in other cases.
The letter shall specify the date, duration and times of the training course and the name of the establishment or organisation responsible.