Таймер работает медленнее положенного

Option Explicit
Dim bState As Byte, nCounter, nTime1, nTime2 As Integer
Private Function Random()
Randomize Timer
Random = Int(Rnd * 1901) + 100
End Function
Private Sub Form_Load()
    bState = 0
    nCounter = 0
End Sub
Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    Select Case bState
    Case 0
        Randomize (Timer)
        tmrStart.Interval = Random()
        frmMain.BackColor = &H8080& 'æåëòûé
        nCounter = 0
        bState = 1
        tmrStart.Enabled = True
        Exit Sub
    Case 1
        tmrStart.Enabled = False
        frmMain.BackColor = &H80& 'êðàñíûé
        bState = 0
        Exit Sub
    Case 2
        tmrCounter.Enabled = False
        frmMain.BackColor = &H800000 'ñèíèé
        frmMain.Caption = "Âðåìÿ ðåàêöèè " + Str(nCounter * 10) + " ms"
        bState = 0
    End Select
        
        
End Sub
Private Sub tmrCounter_Timer()
    nCounter = nCounter + 1
    'frmMain.Caption = Str(nCounter*10)
    tmrCounter.Enabled = True
End Sub
Private Sub tmrStart_Timer()
    frmMain.BackColor = &H8000& 'çåëåíûé
    bState = 2
    tmrCounter.Enabled = True
    tmrStart.Enabled = False
End Sub