[Question]Making use of cookies

[iRakic]

But, what I need is my other members ( non staff, non vips ) to see a donation remainder that has a I AGREE (Usually, check it and click continue ).

To do this just make a query to your DB (or some other way) asking what's current user's group, and if it's not in staff or VIPs group then show him that message.
Also if you implement option from your second question, don't forget to check also if user saw message.

How to make the remainder so that it comes up only first visit ?

To do this add a new column in users table where you will store if user saw message or not.

And also, The CONTINUE button, how can I disable it for a certain period of time ? I mean, I want the user to read the page for 30 seconds, after 30 seconds the Continue buttons can be clicked

Make that button as default to be disabled (HTML), and add JS code that will wait for 30 sec, and after that to enable that button.