There isn't a default runtime in the integration app, but I see each device has one set (mine are 15 and 20). And in the BHyve app itself it appears I have 30 on one and 10 on the other. That said, none of these numbers seem to impact my simple use of the integration to turn on a valve and turn it off at any point I'd like later.
My runtime is actually scheduled in my Rachio controller. In Rachio, I have two zones to which have no valve is actually connected but Rachio doesn't know that. And what I have in Hubitat are two rules that mirror the Rachio zones into BHyve. This allows me to use Rachio weather intelligence and scheduling and not use the BHyve app or scheduling at all. Here's one of the mirror rules:
