I'm a nano-planner myself (and a ML, and a serious nano-veteran).

Participating isn't a question for me, so I usually get into gear mid-September. I try to be realistic with my expectations, meaning looking at my work schedule and figure out how much my co-ML and I will be running events together vs apart (she lives about an hour away. We live on exactly the top and bottom of our region) and anything else that might be consuming my time during November.

When I'm busy, I need more notes, a firmer outline, all that stuff. That way, when I have time to write, I can get words on paper instead of thinking about potential words on paper.

I snowflake everything out to a scene list with most of my attention on execution - literally what are they doing and why. My goal is to have a decently complete outline by Nov 1, but since my region does plotting meetups once a week for October, I am better off having my outline before the last week, so I can focus on organising the kick off party, handout packets, and all the like.

If you plot, start now! If you don't, you can still gather inspiration. Keep an eye on your region, and even if they aren't planning any pre-nano events, you can still suggest some informal gatherings either in-person or online.

TL;DR - It's never too early to start planning a nano.