New Post Image Slow at Going Away

[AWMGolfer]

On the SMF forum I used to use the image that showed a forum having a new post would change to showing no new posts as soon as you read the thread. Since switching to vBulletin the image takes a while to change back to showing no new posts. I am sure it is somewhere in the settings but I just can't seem to find the setting I need to change. I tried to find this in other posts but couldn't find anything so thank you in advance for any help!!