Excel: Create ranges for date and blank cells

[Zvoni]

Since you say "Loop" i take it it's vba.
If you're alread in a loop, what's wrong with checking the cells in Column A if they're empty/blank?
Some speed up might be gained with

Public Function GetLastRow(ByVal ASheetName As String, Optional ByVal AColumn As String = "A") As Long
    GetLastRow = Worksheets(ASheetName).Cells(Worksheets(ASheetName).Rows.Count, AColumn).End(xlUp).Row
End Function

Pass the Sheetname, and you get the last non-empty row in column A (for your second range "A7:A50" that would be 7)

Aircode

Public Function GetLastRow(ByVal ASheetName As String, Optional ByVal AColumn As String = "A") As Long
    GetLastRow = Worksheets(ASheetName).Cells(Worksheets(ASheetName).Rows.Count, AColumn).End(xlUp).Row
End Function

Sub SetRangeName(ByRef ASheetName As String)
Dim lr As Long
Dim i As Long
Dim j As Long
Dim c As Long
Dim b As Boolean
Dim ws As Worksheet
Dim arrRanges() As Range
    c = 0
    Set ws = Worksheets(ASheetName)
    ReDim arrRanges(0 To c)
    lr = GetLastRow(ASheetName)
    b = True
    For i = 3 To lr
        If ws.Cells(i, 1) <> "" Then
            If b Then
                j = i
                b = False
            Else
                Set arrRanges(c) = ws.Range("$A$" & j & ":$A$" & i - 1)
                ReDim Preserve arrRanges(0 To c + 1)
                c = UBound(arrRanges)
                j = i
            End If
        End If
    Next
    Set arrRanges(c) = ws.Range("$A$" & lr & ":$A$50")
End Sub

Sub Test()
    SetRangeName "Sheet1"
End Sub