elapsed = minutes(datetime(d2, 'InputFormat', 'HH mm ss') - ...
datetime(d1, 'InputFormat', 'HH mm ss')); %note the difference in format string
As we don't know what your 3rd test is, we can only speculate on the cause of failure. I would suspect it's because 0.016667 is only a crude approximation of 1/60, and for some values the difference is enough to put you over the accuracy threshold required by the test.
You gain nothing by using a multiplication by 0.016667 and it actually makes your code more obscure as the reader now has to check that 0.016667 is a correct approximation for 1/60, so what don't you write it as a division. Makes a lot more sense to me:
m = d(4)*60 + d(5) + d(6)/60; %is a lot more accurate and it's that you're converting seconds into minutes
