This is no big deal. What they are talking about here is the additive cycles in a day and not worrying about the compensation process for that.
Anything connected to the 60Hz power is at 60HZ, You can not connect a 61Hz generator to the grid.
In addition, when you connect a generator to the grid, you have to adjust its phase, as you bring it on line.
If the phase angle does not line up you get you get into a "tug of war" between multiple generation sources and that doesn't work.
The sine wave coming out of one generator has to line up with the other sine waves from the other sine waves from the other generators.
60 cycles/sec X 60 sec/min X 60 mins/hour X 24 hours/day = 5.184E6 cycle/day
What the article is talking about is the adjustment of the generating stations on the grid so that at the end of the day you get that exact number of cycles across the grid, not one more not one less. It is "really close" without tweaking but not exact.
It costs money to do those tweaks, to get the numbers on the money. That tweak right now really doesn't serve much purpose anymore.
Noting exciting, or interesting here, this is not Y2K nonsense, move along...