Dear All

I want to be able to create a demo version of an application which has an
activation code which will 'expire' the demo either:
a) on a certain date I specify or
b) at the end of 30-60 days.
(I know that these are two different things)

Is there any recognized way of doing this sort of thing using product
activation codes?

Url's, documentation links, published articles?

Any other suggested methods?

Thanks

Amul