what is the difference between 1 harakah and 2 harakah?

Question
what is the difference between 1 harakah and 2 harakah? In hafs by the way of shatibiyyah you can do madd munfassil/muttassil 4 or 5 harakah but what is the difference between them, it seems that 5 harakah is 0.1 seconds longer than 4 harakah.
If in alhamdu  the `du` is 1 harakah then in `min doonillah` would `doo` be 2 harakah.?

Answer
The time of a harakah totally depends on the speed of the reader and we base all mudood on the time the reader takes to say one vowel and multiply it.  One reader's timing is not necessarily equal to another's as far as seconds, in fact in most cases it is not; it depends on how fast or slow the reader is reading and then the mudood are based on multiples of that. We can not measure it in seconds or portions of seconds.
You example is correct, the time it takes to read one vowel, such as a dhammah is multiplied by two to get the time of a natural medd (two vowel counts).