rules userpoints and flag

Hello,
I am using the Flag and User points module.
I have set a rule that when user have Flagged some content he lose 15 points.
All work just fine, but now I wold like to wright 2 rule's:
The first one is a rule that hide the flag if the user has lass then 15 points and show the flag if he has 15 or more.
The second one is that check's every 4 days if user have lass then 15 points and grand his account with 15 points.
I tested some triggers like when user has log in, but users doesn't always log out as they closing the browser.

In witch way I should do that?

Thanks.