Fix pipe to calculate difference between time-out and time-in

SubstractDatePipe is being used to calculate the number of hours/minutes representing the difference between time-out and time-in. This pipe has a bug since it is not considering the dates, only the times.

For example:
```
start-date: 13/05/2020T10:00:000Z
end-date: 14/05/2020T12:00:000Z
```
The result is going to be 2 hours which is wrong since the right value should be 26 hours.

Locate the SubstractDatePipe and inspect how it derives the difference from the supplied dates. Reproduce the example with start-date 13/05/2020T10:00:000Z and end-date 14/05/2020T12:00:000Z, then verify that the result accounts for the date boundary and reports 26 hours rather than 2.

Written by the indexing model from the issue text.