As per your requirement, what I see, you cannot check the online server for date.
This is quite obvious for offline system.
So, you need to do few things -
set the registration date and expirydate in the form of high encypted data and save it somewhere in registry database.
While the Application opens each time, get the latest clock date and save the encrypted data in registry.
Ensure to check the Clock date and the Last Usage Date. If last usagedate < clockdate, then everything fine but if usagedate>clockdate, user has changed the clock date. So, don't update the registry.
Once the lastusagedate reaches the expiry date, pops a message "Your Trial has been expired.".
Hope this helps.
cheers
