Second representation requires at least 6 bits to represent numbers between 0 to 59. But 5 bits are not just enough - 25 = 32, which can only represent from 0 up to 31 seconds.
According to K.N. King:
You may be wondering how it 's possible to store the seconds - a number between 0 and 59 in a field with only 5 bits. Well. DOS cheats: it divides the number of seconds by 2, so the seconds member is actually between 0 and 29.
That really makes no sense?
Yeah, I have been trying to work out a table for just the seconds, and yeah, the 5 bits isn’t enough. I wasn’t thinking it through. Another bit would be needed to be able to capture the flip, and in that case the extra bit would just allow you to store the actual 0-59 value. That’s what I get for speaking before I have worked it out in my head.