no more data posts within 30 second. how to do that

[Oracle simsim]

Hello

I have made a mini plugin that enable my members to choose their mood directly from the a button in the header. when that button pressed the following happen:

1- a prompt box will be shown asking the member about his mood
2- if member write something, an ajax post request will be sent to the server.
3 using a plugin in misc.php, the request will be validated and processed then update the associated userfiled.

I want to prevent members to change their moods frequently . I mean if any member request to change his/her mood. it will not be allowed to change it again within 30 second or less or more.

how vbulletin prevent the user from writing another post with 30 second ? same idea

forgive my weak English and bad title. Any small information will be helpful.