Hi Asad,
I believe this is only a display issue to be fixed in the resource file.
When we adjust times we are using DateTime.AddHours(3.5) which is correct, it is 3 and 1 half hours because the decimal is base 10 it is not a number representing hours and minutes,it is a number representing hours and fractions of hours and .5 is half an hour or equivalent to 30 minutes.
Even the resources are currently listing it in decimal format like +3.50 rather than +3:30, I will change the resources to hour and minute notation as that may be easier to understand in the UI.
Best,
Joe