Option Explicit
Dim CheckTimer      As Date

Sub CheckTask()
    Dim i           As Long
    Dim rDate    As Date
    Dim rTime    As Date

    Dim curDate As Date
    curDate = Date

    Dim curTime As Date
    curTime = Time

    With ThisWorkbook.Worksheets("КАЛЕНДАРЬ")

        For i = 9 To .Cells(.Rows.Count, "G").End(xlUp).Row
            rDate = .Cells(i, "G").Value
            rTime = .Cells(i, "H").Value

            If IsDate(rDate) And IsDate(rTime) Then

                If rDate = curDate And curTime >= rTime And curTime < rTime + TimeSerial(0, 1, 0) Then
                    MsgBox "Время вышло! Примите меры Уважаемый!", vbCritical
                    Exit For
                End If

            End If

        Next i

    End With

    StartChecking
End Sub

Sub StartChecking()

    On Error Resume Next
    Application.OnTime EarliestTime:=CheckTimer, Procedure:="CheckTask", Schedule:=False
    On Error GoTo 0

    CheckTimer = Now + TimeSerial(0, 1, 0)
    Application.OnTime EarliestTime:=CheckTimer, Procedure:="CheckTask", Schedule:=True
End Sub

Sub StopChecking()

    On Error Resume Next
    Application.OnTime EarliestTime:=CheckTimer, Procedure:="CheckTask", Schedule:=False
    On Error GoTo 0
End Sub

=ТДАТА()>=(A5+B5)