Date and time picker

Hi

Please help

I am designing a form that requires a date and time field to calculate the full number of hours.
This could be the same day but this could also be 2 days later.

Please see the excel example.

I have managed to find the activeX controls for date and time however getting this information to a cell that i can calculate from does not seem to work. (colomn h)
An i would like to have is as user friendly as possible.
I have tried to use the excel dates but this requires the user to fill in the cell with the correct format and this does not always happen.

Does anyone have any ideas?

Cheers,