There is somewhat of a trick or an art to using an excluder.
Bees don't like honey in the broodnest.
Bees like honey above the brood.
The time for an excluder is just as a nectar flow starts.
Two boxes crowded with bees, as a nectar flow is coming.
Make bottom box be the honey frames, filling in with sealed brood.
Make the next box up be the frames of eggs and larva, filling in with what's left.
In that top box, now remove 2 frames that are mostly empty or of older brood. Put in 2 frames foundation or comb to the two outside positions.
Now put on the excluder, adding a box of foundation on top, with those two drawn frames in the middle of it. These are the 'bait frames'.
Add another super on top, with the top covers.
There is now honey under the brood, in the broodnest. There is space above the brood to store honey, over excluder. The bees will start moving that honey from under the brood up above the brood, above the excluder to store above the brood. They are encouraged to do so also because there is two bait frames of open brood up there that they need to take care of. They will need to start drawing frames next to it for storing nectar to feed the brood. As those two frames emerge, they'll be filled with honey, and drawing of comb honey will continue above the excluder until the nectar flow slows or stops.