I think that there is some value in calculating the time it takes for the group to go from one participant to many participants to see if there is an exponential growth rate taking place.

It's midnight and well, I decided to do just this at 5 second intervals and then count the number of people dancing (and also flocking too the party, ie in the frame), just to get a rough idea.

  0 seconds   - 1
  5 seconds   - 1
  10 seconds  - 1
  15 seconds  - 1
  20 seconds  - 2
  25 seconds  - 2
  30 seconds  - 2
  35 seconds  - 2
  40 seconds  - 2
  45 seconds  - 2
  50 seconds  - 2
  55 seconds  - 3
  60 seconds  - 3
  65 seconds  - 3
  70 seconds  - 3
  75 seconds  - 7
  80 seconds  - 11
  85 seconds  - 17
  90 seconds  - 21
  95 seconds  - 26
  100 seconds - 35
  105 seconds - 46
  110 seconds - 59

At this point, it became too difficult to count the number of people joining it every frame, but the data seems to indicate exponential growth.

(I'm also assuming Guy #1 was dancing for some time on his own before the person with the camera decided to film it, so this would show the exponential growth more)