What is the busiest month of the year in sitdown restaurants and slowest month of the year in resturants?

I grew up in a holiday area. Our season is pretty May to end of August. There are some more dedicated tourist that come in September / October. In reality, you are looking to make most of the years money in the season and then fall back to local trade outside of that. Some places have a winter season, others may have a season that is kind of either side of summer due to extreme heat.

Some places, like Las Vegas, kind of have this organised. Conference season is usually not peak summer. Big conferences attract lots of people, CES has about 180,000 attendees and SHOT show about 60,000. Both of those are in January. Big fights, big bands, Chinese New Year, Spring Break and all manner of other events drag in the crowds too.

We live in a industrial area now. The real busy seasons tend to the run up to Christmas. Summer time sees a lot of people going on holiday and it quietens down. Add in any large TV sporting events and sitdown restaurants will not be busy. You can even look at the pay cycles of large local employers to understand when the next good weekend will be.