Which month is best to start a daycare?

My kid will be 12 month old in august and has secured a spot at a daycare starting September. As the days gets closer, I am getting anxious. We have a nanny full time for him right now and are not sure if we want to transition him yo daycare at 12 months or 18 months (around March) If we start him in sept, he’ll be 12 month old, may not be walking yet, definitely not communication and it’s right at the start of the flu season.

If we start in March, he’ll be 18 month old, will be walking and may be saying a few words. It’ll be almost end of winter. Our concern with this option is him getting bored at home throughout winter, or is not getting a spot again in March.

Husband and I both have demanding jobs 9-5.

What’s the best month to start a daycare? Would starting daycare in September at 12 months be a disaster?