I did the same process, much for the same reasons, as I couldn't work out when I could start imaging because things were behind trees etc.
I did a short video on this. I wasn't super accurate and tried to err on the side of caution, but it has given me way better ideas of when I can start (and stop) imaging depanding on where I'm pointing.
https://youtu.be/L2POt_xYA_g