When should I apply for the Certificate of Entry (C.O.E.) for my flight to Thailand?

The user seeks clarification on whether they need to wait until 15 days before their flight to apply for the Certificate of Entry (C.O.E.) for a flight scheduled on July 15. Comments indicate that one can apply earlier if they have confirmed travel plans and that the application process for the C.O.E. will officially open on June 28, though early submission of forms appears possible.