timeFind.vbs

Function truncDate(t As Date) As Date
    truncDate = TimeSerial(Hour(t), Minute(t), 0)
End Function

Function findTime(r As Long, c As Long) As Long
    findTime = Application.WorksheetFunction.Match(CDbl(truncDate(Cells(r, c))), Range("2:2"), 1)
End Function

Sub t()
    Dim cs As Long
    Dim ce As Long
    Dim c As Long
    Dim r As Long
    Dim MaxRow As Long
    MaxRow = Cells(3, 1).End(xlDown).Row
    
    For r = 3 To MaxRow
        cs = findTime(r, 1)
        ce = findTime(r, 2)
        For c = cs To ce
            Cells(r, c).Value = "o"
        Next
    Next
End Sub