I think you’d need the following:
- Save the installation date (Either on a localDB or in the registry)
- Identify the current date
If you are going to do by date, you should worry a lot about the restriction, because if the user changes the date may give problem, and if you take the date of a Webservice you will require the user to be logged in.
I did something similar a while ago, but I didn’t care much about the date control, I did the following:
The user can use for 30 days or X Uses (initializations).
When starting the system, I check if the date has passed, if it has not passed, I check if the uses have passed. Save the uses on a counter on a localDB along with the app information.
This was the best way, and the fastest I found to do something similar to what you are wanting.