I'm planning to put Excel on a few users' machines, but I want to set it up
in such a way that Excel won't open if they haven't met some external
conditions.

So they do the usual choice of things to fire up Excel.exe, but if the
conditions aren't met, eg. outside office hours, then they get a message
saying "XYZ Condition not met, etc. Try again later".

I can see how to do this simply using a workbook containing VBa in XLStart,
or perhaps using startup switch on Excel to open such workbook, but my wiley
users would soon find this and delete it.

Is there any way of doing something more robust, such as modifying a dll
that would trigger my test (eg. a little exe file "conditionsmet.exe"), that
if the condition wasn't met Excel would not open?

Any ideas greatly appreciated,
TIA,

Dranz