My Airbnb -> Google calendar has not worked properly since late 2016, @Tom371. The delay is always anything from 2 hours to 12, and I have tried everything the internet suggests to fix that. I experienced no delays at all from 2012 to 2016, so when the trouble started I thought it was temporary. I have tried everything the internet suggests to fix it. It was one of the things that first brought me to this forum. I am afraid I have given up.
Sorry to be of no help, but I wanted you to know it is not just you.
Hopefully someone will write with an answer for both of us!