Kirsty is saying you can START the process right now. It will help you in many ways to do it as soon as you can (using the link she provided).
Once your goods are being manufactured, you will then be able to provide “proof of use” to the Trademark office. They don’t usually request this for a few months anyway, because that’s how long it takes them to file stuff.
So, you can apply for the trademark pretty quickly, and then get the business going in the meantime.