Time difference calculation in Upperforms & Line items

The Client's need:

- Calculate the time spend per site visit by inspector

I created a generic line item BP with line items where the inspector fills out his arrival time and departure time through the date picker. The difference between the two is multiplied with 24 to get the hours. All the line items then add up to a total at the upperform. However, the time calculation does not give the expected time. e.g. between 7 am to 9 am the calculated time is 1.9 hours in stead of 2 hours.

Is this a bug in Unifier?

Any ideas to do the above differently to get the actual time of the site visit?