Everyone eventually accidentally turns on their amp without a load--well most of us at least.
the problem occurs when you hear no music and turn it up, putting harmful currents into the transformers.
If you keep the volume down or on mute or have no signal going in, you won't do any damage. But there is no reason to do this other than by accident. This won't help significantly with burnin although time on the tubes with heat will help them settle in. I'd just wait and do it with music so you can hear the improvements.
Jerry