The NotesDateTime constructor takes the date as a string, so you need to cast the Date value you get from NotesDocument.Created to a string.
Try this:
Dim monBankHolChk As NotesDateTime
Dim friBankHolChk As NotesdateTime
Set friBankHolChk = New NotesDateTime (Cstr(entry.created))
Set monBankHolChk = New NotesDateTime (Cstr(friBankHolChk))
As you see above, I would also suggest to declare the variables as the correct data type from the beginning, don’t use Variant unless it is absolutely needed.
Finally, I would use the variable name ‘doc’ for a NotesDocument object, not ‘entry’. That name I reserve for objects of the type NotesViewEntry. Things like that makes the code easier to read, especially if you have other people looking at it or maintaining it.