Take a look at Tk: Binding Events and Callbacks. Your post is a bit sketchy on details, making a definitive answer difficult; however, Tk::after and Tk::fileevent look to be likely candidates for what you might want; other items in that section may also be useful.

I've written a number of posts over the years which may be relevant to your needs. In many cases I've included fully working scripts. There may be something there to suit your needs or which you can adapt as necessary. You can use this preloaded search (if you're unfamiliar with Super Search, that just preloads the search parameters: click "Search" to get the results).