i made a project. i want to release it. but i want to release a trail version of it for 15 days. any proses. please help

use registry to save trial time.

I think it was detail.
I means to save trial times (expired time) in registry. Compare it with the day when program running.
ex :
a = Today
b = expired time (saved in registry)

if a > b then
' expired message.
' Do nothing

how can i save trial times (expired time) in registry