Guilfordbeekeepers.org

The part of checker boarding that helps with swarming is keeping empty combs between the pollen frames that are on each side of the brood nest. In other words, laying room in the brood nest. Removing the outside frames, moving the non-brood frames outward, and inserting an empty frame between them and the brood will accomplish the same thing. After about may 10th, our last frost, you can put empties IN the brood nest.

I marked may to my calendar as a reminder,
Thanks again sir

I often do it much earlier than May 10. But that's just me.

You can add empties anytime, right next to the brood nest, but I wouldn't separate the brood frames with an empty until after the cold is gone.

Agreed. I just have a sooner opinion of when the "cold" is gone.