Create Trial version Software in c# win form

Hi,

 

I want to create a trial application for few days in c# windows form. I have got some code or links. But I have an question that how to get first installation date. It should be System date or any other. Because if it is system date. Then user can change date at installation time. How it will be manageable?

 

Please help me and send me code or useful links.

 

Thanks in advance.