vb.net subtract two excel cell date and times - vb.net

Question

Hello I have this program that lets you start and stop time on a job the problem I am having now is that if it switches from A.M to P.M while time is tracked the program doesn't work right. so I have a button that puts the Time.Now when its pressed in a excel cell than when you stop the job it puts the End time in another cell and then it go's in and grabs the two cells and subtracts them. what I need it to do is put the Date and Time in the cell then both and only give me the Minutes and hours that it took. here is what I have for code.
'This code is for when you start the job.
'which this is only hours and minutes prob should be
'Date and Time
Dim StartTime As String = DateTime.Now.ToString("h\:mm")
'This line of code puts it in an excel cell
oXL.ActiveCell.Offset(0, 13).Value = StartTime
'This code is for when you end a Job.
'Again its only hours and minutes but prob should be
'Date and Time
Dim EndTime As String = DateTime.Now.ToString("h\:mm")
'This is the Total Time I am going to have
'I used TimeSpan
Dim TotalTime As TimeSpan
'Now this is where I put the End time when the
'Button is clicked.
oXL.ActiveCell.Offset(0, 14).Value = EndTime
'Once Both cells have the start and end Times I get them both with this code.
'Again this should prob be Date and Time.
Dim time1 = TimeSpan.ParseExact(oXL.ActiveCell.Offset(0, 13).Value, "h\:mm", CultureInfo.CurrentCulture)
Dim time2 = TimeSpan.ParseExact(oXL.ActiveCell.Offset(0, 14).Value, "h\:mm", CultureInfo.CurrentCulture)
'I then use this code to do my math.
TotalTime = time2 - time1
The Total time I need i only to be the hour an minutes that it took to do the job.

Answer 1

You are taking two dates, converting them and storing them into string variables, then reading them back into dates to calculate. You are hoping that they are in the right format when you parse them back, this in itself is top heavy. But why store dates as string at all? You can convert a date to a string at any time on the fly with the .ToString() method. Just keep them as dates and write them out to the excel sheet as strings when needed. The values will be the same either way, and you're not relying on your sheet to have the data in the adjacent locations, you will just perform the calculation and you are done.
'This code is for when you start the job.
'which this is only hours and minutes prob should be
'Date and Time
Dim StartTime As DateTime = DateTime.Now
'This line of code puts it in an excel cell
oXL.ActiveCell.Offset(0, 13).Value = StartTime.ToString("h\:mm")
'This code is for when you end a Job.
'Again its only hours and minutes but prob should be
'Date and Time
Dim EndTime As DateTime = DateTime.Now
'Now this is where I put the End time when the
'Button is clicked.
oXL.ActiveCell.Offset(0, 14).Value = EndTime.ToString("h\:mm")
'Once Both cells have the start and end Times I get them both with this code.
'Again this should prob be Date and Time.
' Dim time1 = TimeSpan.ParseExact(oXL.ActiveCell.Offset(0, 13).Value, "h\:mm", CultureInfo.CurrentCulture)
' Dim time2 = TimeSpan.ParseExact(oXL.ActiveCell.Offset(0, 14).Value, "h\:mm", CultureInfo.CurrentCulture)
'This is the Total Time I am going to have
'I used TimeSpan
Dim TotalTime As TimeSpan
'I then use this code to do my math.
TotalTime = EndTime.Subtract(StartTime)
'output time difference
MsgBox(TotalTime.ToString)
.:EDIT:.
To give you an example of total hours and minutes:
Dim startTime As DateTime = DateTime.Now 'read from excel instead
Dim endTime As DateTime = DateTime.Now.AddDays(1.5).AddMinutes(60) 'read from excel
Dim span As TimeSpan
span = endTime.Subtract(startTime)
MessageBox.Show("Total Hours: " & (span.Days * 24) + span.Hours & ", Total Mins: " & span.Minutes)

Answer 2

I hope this will be able to assist in your calculation (grabbing a start and end date string, converting it to DateTime, then outputting the hours and minutes):
'This code is for when you start the job.
'which this is only hours and minutes prob should be
'Date and Time
Dim StartTime As String = DateTime.Now.ToString("h\:mm")
'This code is for when you end a Job.
'Again its only hours and minutes but prob should be
'Date and Time
Dim EndTime As String = DateTime.Now.AddHours(3.5).ToString("h\:mm")
'This is the Total Time I am going to have
'I used TimeSpan
Dim TotalTime As TimeSpan
'Once Both cells have the start and end Times I get them both with this code.
'Again this should prob be Date and Time.
Dim time1 = DateTime.Parse(StartTime)
Dim time2 = DateTime.Parse(EndTime)
'I then use this code to do my math.
TotalTime = time2 - time1
Dim Hours = TotalTime.Hours
Dim Minutes = TotalTime.Minutes
System.Console.WriteLine(Hours & "h " & Minutes & "m")