Wow I did not expect so many people would pay attention to my
beginner's question!
I have now many different code lines to try.

In you second reply, I mostly appreciated those lines:

Application.ScreenUpdating=False before unhiding and
rehiding, and
Application.ScreenUpdating=True afterwards

because this was one of the reasons I wanted to hide  the sheet:
While the webqueries are updated, (it can take a few seconds) it is
really not very pretty to watch.

So in order to update  them hidden if it works, I could put  a flag
that would tell the user  to be patient while the data  are being
updated.

As to hiding the sheets  I have different codes to try.

All this if it works on my old Excel version (1997), where in the
menu Window I have workbook  hide option, but no sheet  hide.

Which brings me to another question  that I shall post separately.