Just as a test, I turned on my kitchen tap from cold, and it took 1.37 gallons (22 cups) of cold water before the hot was hot. That was with the tap on full.
I also checked the tankless, and it will fire once 0.66gpm are flowing through it. Obviously, any device attached to it shouldn't draw at a rate less than that. The device should also draw "constantly" or in chunks at a time, and not tiny little sips since the tankless needs that second to fire itself up (this is what kills our HE clothes washer).
Some dishwashers have a flow water heater which should pump the temperature up, but the Bosch's also use the hot water for a condensation drying process, and that's where they say the tankless will falter.