Spanish restar fechas.

        Dim Date1 As String = "07/15/2015"
        Dim Time1 As String = "12:54:33"
        Dim Date2 As String = "07/19/2015"
        Dim Time2 As String = "12:50:33"
       
        DateTime.DateFormat="MM/dd/yyyy"    'Ojo con las mayusculas y minúsculas!
       
'====================================================
'Cálculo de los dias como multiplos enteros de 24 horas (tiene en cuenta la hora del día)
'====================================================
        Dim ticks1 As Long =DateTime.DateTimeParse(Date1,Time1)
        Dim ticks2 As Long=DateTime.DateTimeParse(Date2,Time2)
        Dim ellapsedTime As Long = ticks2-ticks1
       
        Dim numDays As Int  = ellapsedTime/DateTime.TicksPerDay
        Dim numHours As Int =(ellapsedTime mod DateTime.TicksPerDay)/DateTime.TicksPerHour
        Dim numMins As Int =(ellapsedTime mod DateTime.TicksPerHour)/DateTime.TicksPerMinute
       
        Log ("Dias   :"& numDays)      '<---- Dará 3
        Log ("Horas  :"& numHours)    ' 23
        Log ("Minutos:"& numMins)     ' 56

'======================================================
'Cálculo de los días restando solamente las fechas 
'======================================================
       
        Dim numDays As Int  = (DateTime.DateParse(Date2)-DateTime.DateParse(Date1))/DateTime.TicksPerDay
        Log ("Dias Reales  :"& numDays)    ' <---- 4