Work hours calculating start and end times

I have made a userform that returns a time value into the cells and those cells are formatted to the time value the reason for F142 and G142 is that is just where I happened to be when I thought that I would try to create this formula. Do you think it is the way it was set up in the userform? My first intention was to do the calculations within the form but I am a newbie to VBA, that would make seasoned users cringe by the sight of my codes :/ and when I do it the other way as Jeff has suggested I get a negative number. I have attached my workbook if that helps I was just trying to create the formula on the excel employee timesheet tab.