Add minutes to an existing countdown timer - vb.net

Question

how To add minutes to an existing countdown timer like while the timer is counting down I can add 10 mins with a push of a button so the time pluses like if the displayed time is 9.59 with the press of a button the time should display 19.59 and continue counting down
Public Class TIMER
Private alarmtime As Date
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
If alarmtime < Date.Now Then
Me.Timer1.Stop()
MessageBox.Show("Time up")
Else
Dim remainingtime As TimeSpan = Me.alarmtime.Subtract(Date.Now)
Me.Label1.Text = String.Format("{0}:{1:d2}:{2:d2}", _
remainingtime.Hours, _
remainingtime.Minutes, _
remainingtime.Seconds)
End If
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
If RadioButton1.Checked = True Then
Me.alarmtime = Date.Now.AddHours(TextBox1.Text)
Me.Timer1.Start()
ElseIf RadioButton2.Checked = True Then
Me.alarmtime = Date.Now.AddMinutes(TextBox1.Text)
Me.Timer1.Start()
ElseIf RadioButton3.Checked = True Then
Me.alarmtime = Date.Now.AddSeconds(TextBox1.Text)
Me.Timer1.Start()
End If
End Sub
Private Sub GameTIMER_Load(sender As Object, e As EventArgs) Handles MyBase.Load
End Sub
End Class
its just a basic countdown timer it works fine all I need for it to do is add minutes to it while its is counting down because when the timer is up I have to click the text box type in the number then press ok then the timer starts so instead off writhing in the textbox I just want to press a button and the countdown timer automatically adds lets say 10 minutes to current time being displayed while its counting down

Answer 1

If you're talking about a normal Timer, this should be your answer:
Me.Timer1.Interval += (60000 * 10)
EDIT:
Try stopping it first:
Me.Timer1.Stop()
Me.Timer1.Interval += (60000 * 10)
Me.Timer1.Start()