Same here on my new 2017. The delay is significantly longer than my previous 01 Ram which was instantaneous. I have assumed it is due to the complete electronic nature of the vehicle. It is long enough that it almost seems useless in an emergency situation as by the time it honks the issues is already over or to late to stop it. I guess that may be over dramatizing it but it is well longer than I would like.
My air horns that were on my previous truck will be going on in short order and will not be going through the oem horn circuit.
2016 Jayco 28.5 RLTS