Extract a time from a cell with date and time stamp and then perform calculations

Hi - I have two cells in a row, each has a date stamp of "01/01/1900". In addition to that date stamp, the first cell has a start time and the other cell has an end time. I am interested in a formula that extracts the time from the two cells and then allows me to perform some simple time of day calculations between the start and end times of the two date stamps

I have attached a workbook with some sample data and an indication of the formula I would appreciate your help in developing.

many thanks