Can I send in a tax year 2023 form now before the end of the year?

In funding a 529 plan, I accidentally added a little more than the gift limit, and need to file a Form 709. I know I have to file that by mail. I'd love to get confirmation that it's resolved. 

 

Can I send it in early? How will I know that it's been received and accepted? 

 

Here's the form, if that's helpful:

https://www.irs.gov/pub/irs-pdf/f709.pdf