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You can use Registry to store the Date of installation in an Encrypted format and retrieve that date when the program loads and decrypt the Date and get what is the time of the system so that you know how many days have passed. Also check that current Date is not anything less than setup date and also its not more than certain range.
You can also protect the date in a form like when OS starts your application start you can wipe out the registry and when that application ends you can write that back so that no one can find that and temper it.
I am not sure what can be done on MAC.