When should I file my trademark application?

Public use of your trademark, at least in the Canadian context, starts to create or crystallize common-law rights in the name that you choose to use, which can be formalized by registration is a federal trademark.  There is a benefit to filing your trademark application sooner rather than later however insofar as it will create public notice of your intentions and claimed rights in the trademark as well as potentially creating a bar in the trademark register to a following third party who wished to protect a similar trademark in your channel of trade.