What is the significance of the date of filing of a trade mark application under the Trade Marks Act,…

The filing date fixes the order of rights between competing applications: an "earlier trade mark" under the Explanation to section 11 is judged by the date of application, and under section 23(1) a mark "shall be registered as of the date of the making of the said application".

The filing date is not the date of advertisement in the Trade Marks Journal (that comes later under section 20), and fees depend on the class and the type of applicant, not on the date.