This IF is like some made up scheme and not LoRaWAN.
Rx1 is the delay from the end of the Tx. It does not relate to processing time - how would the node know how long it takes TTN to process?
https://www.thethingsnetwork.org/docs/lorawan/classes/#class-a
Rather than guessing and using up volunteer time, why not get some logs together?
Thank you Nick, will do that. 
I can not ask a new question, so I will reuse this one.
I do not reliably get downlink messages. In fact, I would say its more likely to not work than work.
Uplink messages are received regularly at 3 minute intervals. Downlink message are checked for five seconds after an uplink. I figure that should cover the two 1 second windows for downlink.
However 99% of the time they are missed.
With that said, I don’t see any documentation on the operation of the downlink queue. If you put a message/payload in the queue, does it get transmitted in 1s, 5s, or 15s? Does it get sent once? Twice?
What does the UI Control “confirm downlink checkbox” do? It does not seem to do anything different.