Function MyFunc(ByVal mDays As String, ByVal mDay As String) As Boolean
Dim xDay( 1  To  7 ) As String, i As Integer, i1 As Integer, res() As String, mReturn As Boolean
Dim day1 As Integer, day2 As Integer, day3 As Integer
mDays = Replace(mDays, " ", ""): mDay = Replace(mDay, " ", "") ' удаление пробелов
xDay( 1 ) = "пн": xDay( 2 ) = "вт":: xDay( 3 ) = "ср": xDay( 4 ) = "чт"
xDay( 5 ) = "пт": xDay( 6 ) = "сб": xDay( 7 ) = "вс"
mReturn = False
res = Split(mDays, ",")
For i =  0  To UBound(res)
    If res(i) Like "??-??" Then
        For i1 =  1  To  7 
            If Mid(res(i),  1 ,  2 ) = xDay(i1) Then day2 = i1
            If Mid(res(i),  4 ,  2 ) = xDay(i1) Then day3 = i1
            If mDay = xDay(i1) Then day1 = i1
        Next
        If day2 <= day1 And day1 <= day3 Then mReturn = True
    End If
    If res(i) Like "??" And (res(i) = mDay) Then mReturn = True
Next
MyFunc = mReturn
End Function

MsgBox MyFunc("ср", "ср")
MsgBox MyFunc("ср, сб", "ср")
MsgBox MyFunc("пн-вс", "ср")
MsgBox MyFunc("пн-ср,пт", "ср")
MsgBox MyFunc("пн,ср-пт,вс", "пт")