This is only a guess, and could be very wide of the mark.
On Fast speed the timer counts down in three-minute segments. My guess is that if the game is paused at the end of one of the segments the timer doesn't move down, and nothing happens to the timer when the game is unpaused. If the game is again paused when the next segment is due, again nothing will happen. Only if the game is running normally will it count down.
On other speeds the timer counts down in larger segments. Although the likelihood of the game being paused at that moment when it is due to count down is less, the time which is in effect added on is more.
Arnie, her is another observation in regards to timing. When a Pg female is ready to drop her child it reads; "0" time left. With the setting on normal time the child doesn't drop till 15 min later. On fast time the child drops within minutes of the time showing "0".
That, I believe, is where your quoted analysis comes in. Perhaps the larger segments, you mentioned, counts in 15 min intervals!
Or am I way off the mark?