Pages, need help

I've just loaded Pages. I need some clarification on the Insert "Date
Time"

On the drop down window the "update each time opened" is checked and
blue.
I keep a continuous doc and do not want either the date nor time to
update.
Is there a way to make, do not update with each opening, the default
for, at least that document?

If that is not possible, what is the exact sequence ensure that when I
enter a date or time that I can ensure it will not update?

I've had, to put it mildly, mixed success with "unchecking" the "Allow
up date" button. Some date and times have held at subsequence openings
and some have not and I cannot determine what, if anything, was
different in my sequence of "unchecking"

Michael