Help with system.outofmemory error - Do While Loop

I'm sure this is something simple but I just don't see it.  I'm getting a system.outofmemory error when I execute this script.  Can someone have a look at it and tell me what I'm doing incorrectly.  

Dim dt As New DataTable
        dt.Columns.Add("Times", GetType(String))

        Dim startTime As DateTime = "12:00 AM"

        Dim row As DataRow
        row = dt.NewRow()
        row("Times") = startTime
        dt.Rows.Add(row)

        Do While startTime <> "11:30 PM"
            row = dt.NewRow()
            startTime = startTime.AddMinutes(30)
            row("Times") = startTime
            dt.Rows.Add(row)
        Loop

        GridView1.DataSource = dt
        GridView1.DataBind()

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