This is from my thread 'setting up a trap out"
>>>>On the day of the setup, I will remove a frame of brood, WITH EGGS,
from my chosen hive, and place it in a warm, shaded area, like the cab
of my truck. On site, I set the platform, level from side to side,
tilted slightly to the front. I then set the catch box where the
"porch" area can be slid against the plywood cone mount, an inch or
two below the bottom of the wire cone.I want the bees to walk from the
cone mount to the box, not fly. Next, I place the frame of brood in
the catch box, with one empty frame between it and the side of the box <<<<
If you set the trap on a warm day when there are foragers in the field and get the cone on by 1 or 2 PM, there will be enough in the trap the first night to keep the brood warm.
As for the bees being left on the comb, I don't think it matters. I have done it both ways. If the hive you take the frame from isn't a real strong hive, you may hurt it by taking a frame of bees and brood. That would be the deciding factor for me.