I tried ActiveCell.Formula and that worked.
It is not necessary to actually Select anything. I was able to set formula in each cell with this:
Sub AGS_Date()
Dim r As Integer
r = Range("A" & Rows.Count).End(xlUp).Row
Columns("A:A").Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Range("A1").Value = "Time"
Range("A2:A" & r).Formula = "=DATE(LEFT(B2,4),MID(B2,5,2),MID(B2,7,2)) + TIME(MID(B2,10,2), MID(B2,12,2), MID(B2,14,2))+MID(B2,16,4)/86400"
Range("A2:A" & r).NumberFormat = "0.0000000000"
'Range("A2:A" & r).NumberFormat = "yyyy-mm-dd hh:mm:ss AM/PM"
End Sub
Why replace formula with values? But if you must:
Columns("A").Copy
Columns("A").PasteSpecial xlPasteValues
Application.CutCopyMode = False
Range("A1").Select