Hi Pearlyn, there is not fix period to when you can start your renovation.
Generally, I would recommend between 3 to 6 months. There are often many details which first-time homeowners can overlook when working on their renovation. It is better to give yourself ample time to make changes and revisions throughout the renovation process since the more you research and gain knowledge about your renovation, the final choice of your renovation would probably evolve from your initial plans/ideas.
Nevertheless, feel free to start speaking to designers anytime. Due to the current covid-situation and lack of manpower, I have also heard from friends that some firms have a long backlog too. Might be also good to at least check with their availability.