Hi Stewart, 
I hope you are doing well. I’m sorry for taking so long to answer, but I was on holidays and it was very hard to have a stable internet connection to answer emails/questions.
The pulse-length is obtained with the Arduino Receive Advanced Demo from the RC Switch library. 
https://rntlab.com/controlling-outlets-optional/
It’s shown on minute 4:32 in the video and in my case the pulse length is 416.
I hope this helps and thank you for your patience,
Rui