ajaxWatchlist (source code) is a script that automatically updates your watchlist. After installing it and browsing to Special:Watchlist, new changes to pages on your watchlist will magically appear, no reloading necessary. To install it, add {{subst:js|User:Theopolisme/Scripts/ajaxWatchlist.js}} to your common.js page and clear your cache.
Custom refresh time
editBy default, new items are loaded every 20 seconds. To change this, add the following text to the top of your common.js page
window.watchlistUpdateFrequency = ???;
with ??? replaced by the desired refresh frequency (in milliseconds: 20000 = 20 seconds).