The usual guideline is to feed as much as the BD will eat in 10 minutes.
Mine fill up sooner than that, and as soon as they slow down, ignore one of the Dubia or act like they are having trouble catching it, I stop feeding. I normally either hand the Dubia to my BDs or drop them into the feeding enclosure one at a time. I usually start them in the morning on salad, then feed Dubia at least twice later in the day.
They will both eat more being hand fed than having to catch the Dubia themselves. :roll: