jQuery function that modifies a DIV
I'm not sure how you would shorten this code. However I think that callback is a terrible name for a function that fades a CSS class. Remember that a function signature should represent what a function does and with that said I would rename it to something like fadeUpdateNotification().

And in the fashion of fading you could replace .show() with .fadeIn() to have the div fade in and out - I dunno how your styling/website looks like but that might look nice...