Tcl - 32 bytes
I noticed that some of these submissions, like the shell or javascript ones, allow you to type the code into the console. If that's the case I can shorten it to:
wm ti . hello\ world;af 3000 exi
Must be typed into the console after running wish. Meaning, run wish without arguments which will give you a REPL console and then type the code above. This makes use of the fact that tcl can be lenient and autocomplete command/function names but only in interactive mode. So that af actually exectues the after command and exi executes exit. I wanted to use ex but my system has the ex editor installed.
Original submission - 36 bytes
wm ti . hello\ world;after 3000 exit
Run using wish instead of tclsh.