Thanks so much Jacob and Rick.

Can I get the macro to run automatically directly upon entering a date
in A1 at all?

Rick Rothstein wrote:
Here is another macro for you to consider...

Sub FillDatesEightTimesEach()
Dim X As Long
For X = 1 To 8 * Day(DateAdd("m", 1, Range("A1").Text) - 1) Step 8
Cells(X, "A").Resize(8, 1).Value = Range("A1").Value + Int(X / 8)
Next
End Sub