Subtracting Hours and Minutes from DateTime not working

I am trying to subtract hours and minutes from a DateTime variable and I have found other posts that show that you should be able to use the .AddHours(-3) in order to achieve this but it is not working for me. I am grabbing the datetime from a DateTimePicker control in vb.net. say the time is 10:00 AM, I want to subtract 3 hours from this to make it 7:00 AM. My hours variable evaluates to -3 but even when I just literally put the number -3 inside the .AddHours it still does not subtract the time. Heres the code

Dim ApptTime As DateTime = Convert.ToDateTime(DateTimePicker2.Value)
        Dim travelTime As String = Label60.Text
        Dim newtime As Double
        Dim split() As String = travelTime.Split(" ")
        If split.Length = 2 Then
            Dim Minutes As String = split(0).Replace("mins", "")
        Else
            Dim Hours As Double = split(0).Replace("Hours", "")
            Dim Minutes As Double = split(2).Replace("mins", "")
            Hours = -Hours
            Minutes = -Minutes
            ApptTime.AddHours(Hours)
            ApptTime.AddMinutes(Minutes)
            Label62.Text = (ApptTime.ToString)