Some of the bees at the entrance to my hive, usually 3 to 5 bees, spend all day doing this…
I put a square box around one of the bees I am talking about. Watch the video and about 5 seconds in the box appears. What are they doing? I have my own guess, but I want to see what you all think.
Washboarding - congratulations, you have adolescent bees who are acting out! 
Nice video of even more doing it here:
Cool! No one knows why? Why are my bees only doing it right near the entrance reducer vs. other parts of the hive?
True, one of the many unsolved mysteries in beekeeping is why they do it, but it seems to be just the adolescents which do it. Maybe some initiation rite before they become foragers!
My guess as to why they are only there, is that your colony is still establishing itself. You probably don’t have a huge population of young bees, yet… So they don’t have to go far to find the space they need to dance. 
And your own guess is what?
I hoped you wouldn’t ask 
. I thought they hated my entrance reducer and were trying to destroy it.
Nice one! I prefer yours!!! 
These are the ocd bees, every hive has them. To get them out of the busy hive,they are told they must stand exactly 2 steps from the entrance to welcome home the foragers. Of course, given their condition, they’re always worried they aren’t close or far enough away 
It’s an interesting phenomenon. Maybe someone will find an answer to the mystery one day. One thing is for sure, they don’t do it for nothing.
They might be conditioning their very complex mouth parts in readiness for an upcoming honey flow.
Saw one if my hives doing it once, thought they were ingesting moisture as it was hot and dry day. Put a few drops of water on the box and they took it, figured that was it but really not sure now.
If anyone finds out post it here right away, very curious.
they were flexing their muscles and seeing who could do more push ups…
Not simple push-ups. Upside down push-ups.
I had to move a whole 2 box hive yesterday from one location to another. After trailering them about 8 miles down the road and letting them settle down a bit as the road was real washboardy; I removed the hardware cloth I used to block the entrance for travel and then put in a reducer so the could get used to their new location for a couple of days. Within in a few minutes of being able to get out again, several bees climbs in the front and did their little dance. I was glad they did it as I had a newbie with me and she thoroughly enjoyed watching the ritual.